Academic literature on the topic 'Sex chromosomes Evolution'
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Journal articles on the topic "Sex chromosomes Evolution"
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Singchat, Worapong, Syed Farhan Ahmad, Nararat Laopichienpong, et al. "Snake W Sex Chromosome: The Shadow of Ancestral Amniote Super-Sex Chromosome." Cells 9, no. 11 (2020): 2386. http://dx.doi.org/10.3390/cells9112386.
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Heteromorphic sex chromosomes, particularly the ZZ/ZW sex chromosome system of birds and some reptiles, undergo evolutionary dynamics distinct from those of autosomes. The W sex chromosome is a unique karyological member of this heteromorphic pair, which has been extensively studied in snakes to explore the origin, evolution, and genetic diversity of amniote sex chromosomes. The snake W sex chromosome offers a fascinating model system to elucidate ancestral trajectories that have resulted in genetic divergence of amniote sex chromosomes. Although the principal mechanism driving evolution of the amniote sex chromosome remains obscure, an emerging hypothesis, supported by studies of W sex chromosomes of squamate reptiles and snakes, suggests that sex chromosomes share varied genomic blocks across several amniote lineages. This implies the possible split of an ancestral super-sex chromosome via chromosomal rearrangements. We review the major findings pertaining to sex chromosomal profiles in amniotes and discuss the evolution of an ancestral super-sex chromosome by collating recent evidence sourced mainly from the snake W sex chromosome analysis. We highlight the role of repeat-mediated sex chromosome conformation and present a genomic landscape of snake Z and W chromosomes, which reveals the relative abundance of major repeats, and identifies the expansion of certain transposable elements. The latest revolution in chromosomics, i.e., complete telomere-to-telomere assembly, offers mechanistic insights into the evolutionary origin of sex chromosomes.
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Camacho, Juan Pedro M., Timothy F. Sharbel, and Leo W. Beukeboom. "B-chromosome evolution." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 355, no. 1394 (2000): 163–78. http://dx.doi.org/10.1098/rstb.2000.0556.
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B chromosomes are extra chromosomes to the standard complement that occur in many organisms. They can originate in a number of ways including derivation from autosomes and sex chromosomes in intraand interspecies crosses. Their subsequent molecular evolution resembles that of univalent sex chromosomes, which involves gene silencing, heterochromatinization and the accumulation of repetitive DNA and transposons. B-chromosome frequencies in populations result from a balance between their transmission rates and their effects on host fitness. Their long-term evolution is considered to be the outcome of selection on the host genome to eliminate B chromosomes or suppress their effects and on the B chromosome's ability to escape through the generation of new variants. Because B chromosomes interact with the standard chromosomes, they can play an important role in genome evolution and may be useful for studying molecular evolutionary processes.
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McAllister, Bryant F. "Sequence Differentiation Associated With an Inversion on the Neo-X Chromosome of Drosophila americana." Genetics 165, no. 3 (2003): 1317–28. http://dx.doi.org/10.1093/genetics/165.3.1317.
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Abstract Sex chromosomes originate from pairs of autosomes that acquire controlling genes in the sex-determining cascade. Universal mechanisms apparently influence the evolution of sex chromosomes, because this chromosomal pair is characteristically heteromorphic in a broad range of organisms. To examine the pattern of initial differentiation between sex chromosomes, sequence analyses were performed on a pair of newly formed sex chromosomes in Drosophila americana. This species has neo-sex chromosomes as a result of a centromeric fusion between the X chromosome and an autosome. Sequences were analyzed from the Alcohol dehydrogenase (Adh), big brain (bib), and timeless (tim) gene regions, which represent separate positions along this pair of neo-sex chromosomes. In the northwestern range of the species, the bib and Adh regions exhibit significant sequence differentiation for neo-X chromosomes relative to neo-Y chromosomes from the same geographic region and other chromosomal populations of D. americana. Furthermore, a nucleotide site defining a common haplotype in bib is shown to be associated with a paracentric inversion [In(4)ab] on the neo-X chromosome, and this inversion suppresses recombination between neo-X and neo-Y chromosomes. These observations are consistent with the inversion acting as a recombination modifier that suppresses exchange between these neo-sex chromosomes, as predicted by models of sex chromosome evolution.
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Sigeman, Hanna, Suvi Ponnikas, Pallavi Chauhan, Elisa Dierickx, M. de L. Brooke, and Bengt Hansson. "Repeated sex chromosome evolution in vertebrates supported by expanded avian sex chromosomes." Proceedings of the Royal Society B: Biological Sciences 286, no. 1916 (2019): 20192051. http://dx.doi.org/10.1098/rspb.2019.2051.
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Sex chromosomes have evolved from the same autosomes multiple times across vertebrates, suggesting that selection for recombination suppression has acted repeatedly and independently on certain genetic backgrounds. Here, we perform comparative genomics of a bird clade (larks and their sister lineage; Alaudidae and Panuridae) where multiple autosome–sex chromosome fusions appear to have formed expanded sex chromosomes. We detected the largest known avian sex chromosome (195.3 Mbp) and show that it originates from fusions between parts of four avian chromosomes: Z, 3, 4A and 5. Within these four chromosomes, we found evidence of five evolutionary strata where recombination had been suppressed at different time points, and show that stratum age explained the divergence rate of Z–W gametologs. Next, we analysed chromosome content and found that chromosome 3 was significantly enriched for genes with predicted sex-related functions. Finally, we demonstrate extensive homology to sex chromosomes in other vertebrate lineages: chromosomes Z, 3, 4A and 5 have independently evolved into sex chromosomes in fish (Z), turtles (Z, 5), lizards (Z, 4A), mammals (Z, 4A) and frogs (Z, 3, 4A, 5). Our results provide insights into and support for repeated evolution of sex chromosomes in vertebrates.
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Charlesworth, Deborah. "Evolution of recombination rates between sex chromosomes." Philosophical Transactions of the Royal Society B: Biological Sciences 372, no. 1736 (2017): 20160456. http://dx.doi.org/10.1098/rstb.2016.0456.
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In species with genetic sex-determination, the chromosomes carrying the sex-determining genes have often evolved non-recombining regions and subsequently evolved the full set of characteristics denoted by the term ‘sex chromosomes’. These include size differences, creating chromosomal heteromorphism, and loss of gene functions from one member of the chromosome pair. Such characteristics and changes have been widely reviewed, and underlie molecular genetic approaches that can detect sex chromosome regions. This review deals mainly with the evolution of new non-recombining regions, focusing on how certain evolutionary situations select for suppressed recombination (rather than the proximate mechanisms causing suppressed recombination between sex chromosomes). Particularly important is the likely involvement of sexually antagonistic polymorphisms in genome regions closely linked to sex-determining loci. These may be responsible for the evolutionary strata of sex chromosomes that have repeatedly formed by recombination suppression evolving across large genome regions. More studies of recently evolved non-recombining sex-determining regions should help to test this hypothesis empirically, and may provide evidence about whether other situations can sometimes lead to sex-linked regions evolving. Similarities with other non-recombining genome regions are discussed briefly, to illustrate common features of the different cases, though no general properties apply to all of them. This article is part of the themed issue ‘Evolutionary causes and consequences of recombination rate variation in sexual organisms’.
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Kratochvíl, Lukáš, Tony Gamble, and Michail Rovatsos. "Sex chromosome evolution among amniotes: is the origin of sex chromosomes non-random?" Philosophical Transactions of the Royal Society B: Biological Sciences 376, no. 1833 (2021): 20200108. http://dx.doi.org/10.1098/rstb.2020.0108.
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Sex chromosomes are a great example of a convergent evolution at the genomic level, having evolved dozens of times just within amniotes. An intriguing question is whether this repeated evolution was random, or whether some ancestral syntenic blocks have significantly higher chance to be co-opted for the role of sex chromosomes owing to their gene content related to gonad development. Here, we summarize current knowledge on the evolutionary history of sex determination and sex chromosomes in amniotes and evaluate the hypothesis of non-random emergence of sex chromosomes. The current data on the origin of sex chromosomes in amniotes suggest that their evolution is indeed non-random. However, this non-random pattern is not very strong, and many syntenic blocks representing putatively independently evolved sex chromosomes are unique. Still, repeatedly co-opted chromosomes are an excellent model system, as independent co-option of the same genomic region for the role of sex chromosome offers a great opportunity for testing evolutionary scenarios on the sex chromosome evolution under the explicit control for the genomic background and gene identity. Future studies should use these systems more to explore the convergent/divergent evolution of sex chromosomes. This article is part of the theme issue ‘Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)’.
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Ping, Jun, Yun Xia, Jianghong Ran, and Xiaomao Zeng. "Heterogeneous Evolution of Sex Chromosomes in the Torrent Frog Genus Amolops." International Journal of Molecular Sciences 23, no. 19 (2022): 11146. http://dx.doi.org/10.3390/ijms231911146.
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In sharp contrast to birds and mammals, in numerous cold-blooded vertebrates, sex chromosomes have been described as homomorphic. This sex chromosome homomorphy has been suggested to result from the high turnovers often observed across deeply diverged clades. However, little is known about the tempo and mode of sex chromosome evolution among the most closely related species. Here, we examined the evolution of sex chromosome among nine species of the torrent frog genus Amolops. We analyzed male and female GBS and RAD-seq from 182 individuals and performed PCR verification for 176 individuals. We identified signatures of sex chromosomes involving two pairs of chromosomes. We found that sex-chromosome homomorphy results from both turnover and X–Y recombination in the Amolops species, which simultaneously exhibits heterogeneous evolution on homologous and non-homologous sex chromosomes. A low turnover rate of non-homologous sex chromosomes exists in these torrent frogs. The ongoing X–Y recombination in homologous sex chromosomes will act as an indispensable force in preventing sex chromosomes from differentiating.
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Sember, Alexandr, Petr Nguyen, Manolo F. Perez, Marie Altmanová, Petr Ráb, and Marcelo de Bello Cioffi. "Multiple sex chromosomes in teleost fishes from a cytogenetic perspective: state of the art and future challenges." Philosophical Transactions of the Royal Society B: Biological Sciences 376, no. 1833 (2021): 20200098. http://dx.doi.org/10.1098/rstb.2020.0098.
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Despite decades of cytogenetic and genomic research of dynamic sex chromosome evolution in teleost fishes, multiple sex chromosomes have been largely neglected. In this review, we compiled available data on teleost multiple sex chromosomes, identified major trends in their evolution and suggest further trajectories in their investigation. In a compiled dataset of 440 verified records of fish sex chromosomes, we counted 75 multiple sex chromosome systems with 60 estimated independent origins. We showed that male-heterogametic systems created by Y-autosome fusion predominate and that multiple sex chromosomes are over-represented in the order Perciformes. We documented a striking difference in patterns of differentiation of sex chromosomes between male and female heterogamety and hypothesize that faster W sex chromosome differentiation may constrain sex chromosome turnover in female-heterogametic systems. We also found no significant association between the mechanism of multiple sex chromosome formation and percentage of uni-armed chromosomes in teleost karyotypes. Last but not least, we hypothesized that interaction between fish populations, which differ in their sex chromosomes, can drive the evolution of multiple sex chromosomes in fishes. This underlines the importance of broader inter-population sampling in studies of fish sex chromosomes. This article is part of the theme issue ‘Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)’.
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Kratochvíl, Lukáš, and Matthias Stöck. "Preface." Philosophical Transactions of the Royal Society B: Biological Sciences 376, no. 1832 (2021): 20200088. http://dx.doi.org/10.1098/rstb.2020.0088.
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This preface introduces the two parts of a theme issue on vertebrate sex chromosome evolution (title below). We invited and edited 22 articles concerning the following main topics (Part 1): sex determination without sex chromosomes and/or governed by epigenetics; origin of sex-determining genes; reasons for differentiation of sex chromosomes and differences in their rates of differentiation as well as (Part 2): co-option of the same linkage groups into sex chromosomes; is differentiation of sex chromosomes a unidirectional pathway?; consequences of differentiated sex chromosomes; differences in differentiation of sex chromosomes under male versus female heterogamety; evolution of sex chromosomes under hybridization and polyploidy. This article is part of the theme issue ‘Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part I)’.
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Meisel, Richard P., Pia U. Olafson, Kiran Adhikari, Felix D. Guerrero, Kranti Konganti, and Joshua B. Benoit. "Sex Chromosome Evolution in Muscid Flies." G3: Genes|Genomes|Genetics 10, no. 4 (2020): 1341–52. http://dx.doi.org/10.1534/g3.119.400923.
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Sex chromosomes and sex determining genes can evolve fast, with the sex-linked chromosomes often differing between closely related species. Population genetics theory has been developed and tested to explain the rapid evolution of sex chromosomes and sex determination. However, we do not know why the sex chromosomes are divergent in some taxa and conserved in others. Addressing this question requires comparing closely related taxa with conserved and divergent sex chromosomes to identify biological features that could explain these differences. Cytological karyotypes suggest that muscid flies (e.g., house fly) and blow flies are such a taxonomic pair. The sex chromosomes appear to differ across muscid species, whereas they are conserved across blow flies. Despite the cytological evidence, we do not know the extent to which muscid sex chromosomes are independently derived along different evolutionary lineages. To address that question, we used genomic and transcriptomic sequence data to identify young sex chromosomes in two closely related muscid species, horn fly (Haematobia irritans) and stable fly (Stomoxys calcitrans). We provide evidence that the nascent sex chromosomes of horn fly and stable fly were derived independently from each other and from the young sex chromosomes of the closely related house fly (Musca domestica). We present three different scenarios that could have given rise to the sex chromosomes of horn fly and stable fly, and we describe how the scenarios could be distinguished. Distinguishing between these scenarios in future work could identify features of muscid genomes that promote sex chromosome divergence.
Dissertations / Theses on the topic "Sex chromosomes Evolution"
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Wright, Alison Elizabeth. "Mating system, sex-specific selection and the evolution of the avian sex chromosomes." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:89079fac-7196-4c15-ac0e-ceae0c4b0264.
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Sex chromosomes experience distinct evolutionary environments, due to their unusual pattern of inheritance, and studies of sex chromosome evolution can shed light on the fundamental evolutionary forces acting across the genome as a whole. Here, I combine genomic and transcriptomic data across a wide range of avian species to explore the evolutionary processes governing sex chromosome evolution. Birds are female heterogametic and therefore it is possible, via comparisons with male heterogametic species, to identify the fundamental factors driving sex chromosome evolution, versus those associated with sex. In this thesis, I uncover a complex mosaic of recombination suppression between the Z and W chromosomes, characterized by repeated and independent divergence of gametologs, together with ongoing genetic exchange. Additionally, I highlight the role of mating system, and interplay between evolutionary forces, in driving coding and expression evolution on the Z and W chromosomes. My findings indicate that although the Z chromosome is masculinized for male-specific effects, the magnitude of genetic drift acting on Z-linked genes is elevated in promiscuous relative to monogamous mating systems. In contrast, evolution of the female-limited W chromosome is governed predominately by purifying selection. Together, my results suggest that the role of the Z chromosome in encoding sexual dimorphisms may be limited, but that W-linked genes play a significant role in female-specific fitness. In conclusion, my findings reveal the power of mating system in shaping broad patterns of genome evolution.
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Jegalian, Karin 1972. "Transition states in the evolution of the mammalian sex chromosomes." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/49625.
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Weingartner, Laura A. "The Evolution of Sex Chromosomes in Papaya (Carica papaya)." Miami University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=miami1280960954.
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Alfaqih, Mahmoud Ahmad. "Mapping and evolution of candidate sex determining loci, sex chromosomes, and sex linked sequences in rainbow and cutthroat trout." Online access for everyone, 2008. http://www.dissertations.wsu.edu/Dissertations/Spring2008/m_alfaqih_042408.pdf.
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Sousa, dos Santos Aretuza. "Molecular cytogenetics and phylogenetic modeling to study chromosome evolution in the araceae and sex chromosomes in the cucurbitaceae." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-174017.
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This study involved the combination of molecular-cytogenetic data and phylogenetic approaches to infer pathways by which chromosome numbers and sizes may have changed during the course of evolution. The two systems for which I generated new data are the monocot plant family Araceae and Coccinia, a genus of Cucurbitaceae. Araceae have about 3800 species in 118 genera, and chromosome numbers range from 2n = 168 to 2n = 8, the latter the lowest number so far and newly reported in my study. The small genus Coccinia includes C. grandis, with the largest known Y chromosome in plants, as documented in my work. The thesis comprises four published or submitted papers.
The first paper reports the result of phylogenetic modeling of chromosome number change along a phylogeny for the Araceae with 113 genera represented. I used a maximum likelihood approach to find the most likely combination of events explaining today’s chromosome numbers in the 113 genera. The permitted events were chromosome gains (i.e. breaks), losses (i.e. fusions), doubling (polyploidization), or fusion of gametes with different ploidy. The best-fitting model inferred an ancestral haploid number of 16 or 18, higher than previously suggested numbers, a large role for chromosome fusion, and a limited role of polyploidization. The sparse taxon sampling and deep age (at least 120 Ma) of the events near the root of Araceae caution against placing too much weight on “ancestral” numbers, but inferred events in more closely related species can be tested with cytogenetic methods, which I did in two further studies (papers 2 and 3).
I selected Typhonium, with 50-60 species, a range of 2n = 8 to 2n = 65 chromosomes. The family-wide study had suggested a reduction from a = 14 to 13 by fusion in Typhonium, but had included relatively few of its species. I built a phylogeny that included 96 species and subspecies sequenced for a nuclear and two chloroplast markers, and then selected 10 species with 2n = 8 to 24 on which to perform fluorescence in situ hybridization (FISH) with three chromosomal probes (5S rDNA, 45S rDNA, and Arabidopsis-like telomeres; paper 2). The results supported chromosome fusion in two species where I found interstitially located telomere repeats (ITRs), which can be a signal of end-to-end fusions, and polyploidization in one species where I found multiple rDNA sites. I then extended my cytological work to other lineages of Araceae, selecting 14 species from 11 genera in key positions in the family phylogeny, which I enlarged to 174 species, adding new chromosome counts and FISH data for 14 species with 2n = 14 to 2n = 60 (paper 3). With the new data, I confirmed descending dysploidy as common in the Araceae, and I found no correlation between the number of rDNA sites and ploidy level (which would have pointed to recent polyploidy). I detected ITRs in three further species, all with 2n = 30. I also discovered gymnosperms-like massive repeat amplification in Anthurium. Similar ITRs are only known from Pinus species.
Paper 4 presents molecular-cytogenetic data for Coccinia grandis, one of a handful of angiosperms with heteromorphic sex chromosomes. The male/female C-value difference in this species is 0.09 pg or 10% of the total genome. My FISH and GISH results revealed that the Y chromosome is heterochromatic, similar to the Y chromosomes of Rumex acetosa, but different from the euchromatic Y chromosome of Silene latifolia; it is more than 2x larger than the largest other chromosome in the genome, making C. grandis an ideal system for sequencing and studying the molecular steps of sex chromosome differentiation in plants.
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MacDonald, Anna Jayne, and n/a. "Sex chromosome microsatellite markers from an Australian marsupial: development, application and evolution." University of Canberra. n/a, 2008. http://erl.canberra.edu.au./public/adt-AUC20081217.122146.
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Microsatellites are simple repetitive DNA sequences that are used as genetic markers
throughout the biological sciences. The high levels of variation observed at microsatellite loci
contribute to their utility in studies at the population and individual levels. This variation is a
consequence of mutations that change the length of microsatellite repeat tracts. Current
understanding suggests that most mutations are caused by polymerase slippage during DNA
replication and lead to changes of a single repeat unit in length, but some changes involving
multiple repeats can also occur. Despite this simplistic overview, there is evidence for
considerable heterogeneity in mutation processes between species, loci and alleles. Such
complex patterns suggest that other mechanisms, including those associated with DNA
recombination, are also involved in the generation of microsatellite mutations. Understanding
which mutational mechanisms are responsible for variation at microsatellite markers is
essential to enable accurate data interpretation in genotyping projects, as many commonly
used statistics assume specific mutation models.
I developed microsatellite markers specific to the X and Y chromosomes and an autosome in
the tammar wallaby, Macropus eugenii, and investigated their evolutionary properties using
two approaches: indirectly, as inferred from population data, and directly, from observation of
mutation events. First, I found that allelic richness increased with repeat length and that two
popular mutation models, the stepwise mutation model and the infinite allele model, were
poor at predicting the number of alleles per locus, particularly when gene diversity was high.
These results suggest that neither model can account for all mutations at tammar wallaby
microsatellites and hint at the involvement of more complex mechanisms than replication
slippage. I also determined levels of variation at each locus in two tammar wallaby
populations. I found that allelic richness was highest for chromosome 2, intermediate for the
X chromosome and lowest for the Y chromosome in both populations. Thus, allelic richness
varied between chromosomes in the manner predicted by their relative exposure to
recombination, although these results may also be explained by the relative effective
population sizes of the chromosomes studied. Second, I used small-pool PCR from sperm
DNA to observe de novo mutation events at three of the most polymorphic autosomal
markers. To determine the reliability of my observations I developed and applied strict criteria
for scoring alleles and mutations at microsatellite loci. I observed mutations at all three
markers, with rate variation between loci. Single step mutations could not be distinguished
because of the limitations of the approach, but 24 multi-step mutations, involving changes of
up to 35 repeat units, were recorded. Many of these mutations involved changes that could not
be explained by the gain or loss of whole repeat units. These results imply that a large number
of mutations at tammar wallaby microsatellites are caused by mechanisms other than
replication slippage and are consistent with a role for recombination in the mutation process.
Taken as a whole, my results provide evidence for complex mutation processes at tammar
wallaby microsatellites. I conclude that careful characterisation of microsatellite mutation
properties should be conducted on a case-by-case basis to determine the most appropriate
mutation models and analysis tools for each locus. In addition, my work has provided a set of
chromosome-specific markers for use in macropod genetic studies, which includes the first
marsupial Y chromosome microsatellites. Sex chromosome microsatellites open a new range
of possibilities for population studies, as they provide opportunities to investigate gene flow
in a male context, to complement data from autosomal and maternally-inherited mitochondrial
markers.
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Carpentier, Fantin. "Evolution des régions non-recombinantes sur les chromosomes de types sexuels chez les champignons du genre Microbotryum." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS428/document.
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Chez les organismes sexués, des suppressions de recombinaison peuvent évoluer dans certaines régions génomiques pour conserver des combinaisons d’allèles bénéfiques, ce qui aboutit à la transmission de plusieurs gènes en un seul locus, alors appelé « supergène ». Les supergènes déterminent des phénotypes complexes, comme l’identité sexuelle chez les organismes qui ont des chromosomes sexuels. Sur certains chromosomes sexuels, la région sans recombinaison s’est étendue plusieurs fois successivement, produisant des « strates évolutives ». Il est communément admis que ces strates évolutives sont issues de liaisons successives de gènes sexuellement antagonistes (qui ont des allèles bénéfiques à un sexe mais délétère à l’autre) à la région qui détermine le sexe, mais peu de preuves empiriques soutiennent cette hypothèse. Les champignons constituent des modèles intéressants pour étudier les causes évolutives des suppressions de recombinaison parce qu’ils peuvent avoir des chromosomes de types sexuels non recombinants sans être associés à des fonctions mâles ou femelles. Dans cette thèse, nous avons étudié l’évolution de la suppression de recombinaison sur les chromosomes de type sexuel chez les champignons castrateurs de plantes du genre Microbotryum. Chez les champignons Microbotryum, les croisements ne sont possibles qu’entre des gamètes qui ont des allèles distincts aux deux locus de types sexuels. Nous avons montré que les suppressions de recombinaison ont évolué plusieurs fois indépendamment pour lier les deux locus de types sexuels, depuis l’état ancestral avec les locus de types sexuels situés sur deux chromosomes différents. La suppression de recombinaison a soit lié les locus de types sexuels à leur centromère respectif, ou a lié les locus de types sexuels entre eux après que des réarrangements chromosomiques, différents dans les différentes espèces, les aient amenés sur le même chromosome. Les deux sortes de suppression de recombinaison sont bénéfiques sous le mode de reproduction par auto-fécondation intra-tétrade de Microbotryum, parce qu’ils augmentent le taux de compatibilité entre gamètes. Les suppressions de recombinaison ont donc évolué plusieurs fois indépendamment via des chemins évolutifs et des changements génomiques différents, ce qui renseigne sur la répétabilité de l’évolution. De plus, nous avons révélé l’existence de strates évolutives sur les chromosomes de type sexuels de plusieurs espèces de Microbotryum, ce qui remet en cause le rôle de l’antagonisme sexuel dans la formation de strates évolutives, les types sexuels n’étant pas associés à des fonctions mâles / femelles. Des études précédentes ont rapporté peu de différences phénotypiques associées aux types sexuels, ce qui rend peu probable qu’une sélection antagoniste existe entre types sexuels sur de nombreux gènes (l’existence de gènes avec des allèles bénéfiques à un type sexuel mais délétère à l’autre). Certains gènes situés dans les régions non-recombinantes des chromosomes de types sexuels étaient différentiellement exprimés entre types sexuels, mais nos analyses suggèrent qu’un tel différentiel d’expression peut être dû à la dégénérescence. En effet, des mutations délétères s’accumulent dans les régions non-recombinantes, ce qui peut modifier l’expression des gènes ou les séquences protéiques. Nous avons donc conclu que la sélection antagoniste ne peut pas expliquer la formation des strates évolutives chez les champignons Microbotryum. Par conséquent, des mécanismes alternatifs doivent être considérés pour expliquer l’extension progressive des régions non-recombinantes, et ces mécanismes pourraient aussi générer des strates évolutives sur les chromosomes sexuels. Ces travaux incitent de futures études à d’une part identifier d’autres strates évolutives qui ne sont pas associées à des fonctions mâles/femelles, et d’autre part à identifier leurs causes évolutives et leurs conséquences en termes de dégénérescence<br>In sexual organisms, recombination suppression can evolve in specific genomic regions to protect beneficial allelic combinations, resulting in the transmission of multiple genes as a single locus, which is called a supergene. Supergenes determine complex phenotypes, such as gender in organisms with sex chromosomes. Some sex chromosomes display successive steps of recombination suppression known as “evolutionary strata”, which are commonly thought to result from the successive linkage of sexually antagonistic genes (i.e. alleles beneficial to one sex but detrimental to the other) to the sex-determining region. There has however been little empirical evidence supporting this hypothesis. Fungi constitute interesting models for studying the evolutionary causes of recombination suppression in sex-related chromosomes, as they can display non-recombining mating-type chromosomes not associated with male/female functions. Here, we studied the evolution of recombination suppression on mating-type chromosomes in the Microbotryum plant-castrating fungi using comparative genomic approaches. In Microbotryum fungi, mating occurs between gametes with distinct alleles at the two mating-type loci, as is typical of basidiomycete fungi. We showed that recombination suppression evolved multiple times independently to link the two mating-type loci from an ancestral state with mating-type loci on two distinct chromosomes. Recombination suppression either linked the mating-type genes to their respective centromere or linked mating-type loci after they were brought onto the same chromosome through genomic rearrangements that differed between species. Both types of linkage are beneficial under the intra-tetrad mating system of Microbotryum fungi as they increase the odds of gamete compatibility. Recombination suppression thus evolved multiple times through distinct evolutionary pathways and distinct genomic changes, which give insights about the repeatability and predictability of evolution. We also reported the existence of independent evolutionary strata on the mating-type chromosomes of several Microbotryum species, which questions the role of sexual antagonism in the stepwise extension of non-recombining regions because mating-types are not associated with male/female functions. Previous studies reported little phenotypic differences associated to mating-types, rending unlikely any antagonistic selection between mating types (i.e. “mating-type antagonism”, with genes having alleles beneficial to one mating-type but detrimental to the other). The genes located in non-recombining regions on the mating-type chromosomes can be differentially expressed between mating types, but our analyses indicated that such differential expression was more likely to result from genomic degeneration than from mating-type antagonism. Deleterious mutations are indeed known to accumulate in non-recombining regions resulting in modifications of gene expression or of protein sequence. We concluded that antagonistic selection cannot explain the formation of evolutionary strata in Microbotryum fungi. Alternative mechanisms must be therefore be considered to explain the stepwise expansion of non-recombining regions, and they could also be important on sex chromosomes. This work thus prompts for future studies to identify further evolutionary strata not associated with male/female functions as well as to elucidate their evolutionary causes and consequences in terms of genomic degeneration
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Santos, Aretuza Sousa dos [Verfasser], and Susanne [Akademischer Betreuer] Renner. "Molecular cytogenetics and phylogenetic modeling to study chromosome evolution in the araceae and sex chromosomes in the cucurbitaceae / Aretuza Sousa dos Santos. Betreuer: Susanne Renner." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2014. http://d-nb.info/1059351285/34.
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Pessia, Eugénie. "Comment le X vient-il à la rescousse du Y ? : évolution de la compensation de dosage des XY humains et autres questions sur l'évolution des chromosomes sexuels eucaryotes." Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10261/document.
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Un premier pan de ma thèse concerne deux différents mécanismes de sauvetage du Y par le X. Premièrement, j'ai participé à une controverse sur la compensation de dosage chez les mammifères. Une hypothèse avait été proposée dans les années 60 par Susumo Ohno, proposant un mécanisme de compensation en deux temps. Chez les mâles, la perte de nombreux gènes sur le Y entraîne un déséquilibre de dosage car ces gènes qui étaient précédemment présents en deux copies sont devenus unicopie, soit une division d'expression par deux. Selon l'hypothèse d'Ohno, chez les mammifères en réponse à cela le X aurait doublé son expression, mais dans les deux sexes menant ainsi à une expression trop élevée chez les femelles. Ce deuxième problème de dosage aurait alors été résolu par la mise en place d'une inactivation aléatoire de l'un des deux X chez les femelles. Tandis que la deuxième partie de l'hypothèse d'Ohno, l'inactivation du X, a été très étudiée, la première partie est restée spéculative jusqu'aux années 2000. En étudiant des données d'expression du X humain j'ai pu montrer, de manière concomitante avec d'autres auteurs, que la première partie de l'hypothèse d'Ohno n'est pas totalement vraie car seule une partie des gènes sont sur-exprimés. J'ai ensuite participé à l'écriture d'une revue visant à donner une explication alternative à la compensation de dosage pour l'évolution de l'inactivation du X chez les femelles mammifères. Deuxièmement, j'ai étudié la présence de conversion génique X-Y dans plusieurs gènes, au sein de nombreuses espèces de primates. Mes travaux me mènent à discuter le fait que ce type d'évènement soit effectivement favorisé par la sélection. Je pose l'hypothèse que ces conversions géniques ont été maintenues de manière neutre. Ces deux travaux ne vont pas dans le sens d'un chromosome X sauvant le Y avec beaucoup de zèle. Dans un dernier temps, m'éloignant des espèces modèles, j'ai étudié les chromosomes sexuels particuliers d'une algue brune : Ectocarpus siliculosus. Cela m'a permis de vérifier si le scénario évolutif actuel des chromosomes sexuels est toujours valide dans un groupe d'eucaryotes séparé des animaux depuis plus d'un milliard d'années<br>The first part of my thesis concerns two different mechanisms of the Y being rescued by the X. Firstly, I contributed to a controversy on mammalian dosage compensation. During the 60s Susumo Ohno hypothesized a two-step dosage compensation mechanism. In males, the high loss of Y-linked genes led to a dosage imbalance: these genes were previously present in two allelic copies and became unicopy, meaning that their expression has been halved. According to Ohno’s hypothesis, in response to this imbalance the mammalian X would have doubled its expression in the two sexes, resulting in a to high expression in females. This second dosage imbalance would have been resolved by the random inactivation of one of the two Xs in females. Whereas the second part of Ohno’s hypothesis, the X-chromosome inactivation, has been well studied, the first part remained speculative until the 2000s. I studied human X-linked expression data and was able to show, concomitantly with other authors, that the first part of Ohno’s hypothesis is not totally true as only some of the X-linked genes are hyperexpressed. I later participated in the writing of a review aiming to give an alternative hypothesis for the evolution of X-chromosome inactivation in mammalian females than dosage compensation. Secondly, I studied signatures of X-Y gene conversion in several genes within numerous primate species. Myresults led me to discuss if these events were indeed selected for. I hypothesize that these gene conversion events occurred in a neutral manner. These two different studies suggest that the X chromosome may not be as much a help for the Y as has been suggested. Lastly, moving away from model species, I studied the peculiar sex chromosomes of a brown alga: Ectocarpus siliculosus. This work allowed me to test if the current hypotheses on sex chromosome evolution still hold in a eukaryotic group that diverged from animals more than one billion years ago
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Saunders, Paul. "Evolution d'un déterminisme du sexe atypique chez un mammifère : causes et conséquences." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS280.
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Le système de déterminisme du sexe des mammifères thériens (XX/XY) est ancien et conservé : toute déviation mène généralement à la stérilité. Cependant, quelques espèces dérogent à la règle. C’est le cas de la souris naine africaine Mus minutoides, qui possède un système de déterminisme polygénique où les mâles sont XY, et les femelles XX, XX* ou X*Y (l’astérisque désigne une mutation sur le X, féminisant les embryons X*Y, et apparue il y a presque 1 million d’années). L’évolution d’un tel système est un paradoxe : les femelles X*Y sont censées faire face à des coûts reproductifs importants (perte d’embryons YY, problèmes de méiose…), qui devraient empêcher le maintien de la mutation. Afin de mieux comprendre l’évolution de ce système, nous avons dans un premier temps cherché à identifier les mécanismes évolutifs impliqués dans l’émergence et le maintien du X*. La combinaison d’une approche empirique et d’une étude théorique basée sur des modèles de génétique des populations a permis de mettre en évidence que deux facteurs participent au maintien du X*: un meilleur succès reproducteur des femelles X*Y et la présence de distorteurs de transmission des chromosomes sexuels mâles (leur Y est transmis majoritairement dans les croisements avec des femelles XX et XX* et leur X avec des femelles X*Y). Ce second facteur est certainement à l’origine de l’émergence de ce système. Nous avons ensuite analysé les conséquences de l’évolution de ce système atypique avec trois chromosomes sexuels d’abord sur le phénotype : alors que les trois types de femelles sont indistinguables morphologiquement, les femelles X*Y présentent un comportement masculinisé (elles sont plus agressives et moins anxieuses), puis sur l’évolution de la séquence et de la structure du X et du X* (basé sur des données de séquençage NGS), mettant en évidence que ces chromosomes ont commencé à diverger. Dans l’ensemble, cette étude permet de mieux comprendre les contraintes agissant sur les systèmes de déterminisme du sexe anciens, et les conditions exceptionnelles pouvant réduire ces contraintes permettant ainsi l’évolution d’un nouveau système de déterminisme du sexe. Elle améliore aussi la compréhension de l’impact du complément en chromosomes sexuels sur le phénotype et renseigne sur les forces évolutives agissant sur les chromosomes sexuels dans ce type de système de déterminisme polygénique<br>Therian mammals have an extremely conserved XX/XY sex determination system. Their highly differentiated and specialised sex chromosomes are thought to prevent any modification; however, a dozen species harbour unconventional systems. In the African pygmy mouse <i>Mus minutoides</i>, all males are XY, and there are three types of females: the usual XX but also XX* and X*Y ones (the asterisk designates a sex reversal mutation on the X chromosome, which evolved almost 1 million years ago). The evolution of such a system is a paradox, as X*Y females are expected to face high reproductive costs (loss of YY embryos, meiotic problems…), which should prevent the maintenance of the mutation. To better understand the evolution of this curious system, we first tried to identify the evolutionary mechanisms involved in the emergence and maintenance of the X*. The combination of empirical data and a theoretical approach based on population genetics models showed that two mechanisms participate in the maintenance of the system: the greater breeding success of X*Y females and the presence of sex chromosome transmission distorters (males transmit their Y more often in crosses with XX or XX* females and their X in crosses with X*Y females), the second mechanism likely being the trigger for the initial spread of the feminising chromosome. We then investigated the consequences of the evolution of this unusual system with three sex chromosomes. First on the phenotype, revealing that despite X*Y females have typical female anatomy and morphology, they resemble males on certain aspects of behaviour: they are more aggressive and less anxious than XX and XX* females. Then on the sequence and structural evolution of the X and X* (based on NGS data), showing that the two chromosomes have started diverging. Altogether, these results shed light on the constraints acting on sex determination systems with highly heteromorphic sex chromosomes and show that rare conditions can loosen these constraints. They also provide valuable insight into the impact of sex chromosome complement on phenotype, and inform on the evolutionary forces acting on sex chromosomes in that kind of polygenic sex determination system
Books on the topic "Sex chromosomes Evolution"
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Takagi, N. Vertebrate Sex Chromosomes (Brain, Behaviour & Evolution). S Karger Pub, 2003.
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S, Wachtel Stephen, and International Conference on Developmental Biology, "Evolutionary Mechanisms in Sex Determination" (1987 : Memphis, Tenn.), eds. Evolutionary mechanisms in sex determination. CRC Press, 1989.
Find full textBook chapters on the topic "Sex chromosomes Evolution"
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Paro, Renato, Ueli Grossniklaus, Raffaella Santoro, and Anton Wutz. "Dosage Compensation Systems." In Introduction to Epigenetics. Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-68670-3_4.
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AbstractThis chapter provides an introduction to chromosome-wide dosage compensation systems. We will examine the evolution of dosage compensation, which is thought to be driven by the appearance of differentiated sex chromosomes. In a subset of species with X chromosomal sex determination or XY sex chromosome systems, expression of X-linked genes is regulated by chromosome-wide modifications that equalize gene expression differences between males and females. The molecular mechanisms of X chromosome-wide dosage compensation have been studied in flies, worms, and mammals. Each of these species uses a distinct dosage compensation strategy with a different molecular mechanism. In the wormCaenorhabditis elegans, gene expression on the two X chromosomes of hermaphrodites is reduced to a level that approximates a single X chromosome in males. The fruit flyDrosophila melanogasterachieves dosage compensation by increased transcription of the single X chromosome in males to a level that is similar to the two X chromosomes in females. Lastly, in mammals, one of the two X chromosomes in female cells is transcriptionally inactive and a single X chromosome is transcribed in both sexes. Studies of dosage compensation systems provide insights into how epigenetic regulation controls gene expression and chromatin organization differentially within a cell.
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Traut, Walther. "Sex Chromosome Evolution: Evidence from Fish, Fly and Moth Species." In Chromosomes Today. Springer Netherlands, 2004. http://dx.doi.org/10.1007/978-94-017-1033-6_8.
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Marshall Graves, Jennifer A., and Paul D. Waters. "Mammalian Sex Chromosome Evolution — The Rise and Fall of the Y Chromosome." In Chromosomes Today. Springer Netherlands, 2004. http://dx.doi.org/10.1007/978-94-017-1033-6_1.
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Steinemann, Manfred, and Sigrid Steinemann. "Enigma of Y chromosome degeneration: Neo-Y and Neo-X chromosomes of Drosophila miranda a model for sex chromosome evolution." In Mutation and Evolution. Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-5210-5_33.
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Marshall Graves, Jennifer A., and Swathi Shetty. "Comparative Genomics of Vertebrates and the Evolution of Sex Chromosomes." In Comparative Genomics. Springer US, 2000. http://dx.doi.org/10.1007/978-1-4615-4657-3_7.
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Evans, Ben J., R. Alexander Pyron, and John J. Wiens. "Polyploidization and Sex Chromosome Evolution in Amphibians." In Polyploidy and Genome Evolution. Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-31442-1_18.
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Charlesworth, Brian. "The Evolution of Chromosomal Sex Determination." In The Genetics and Biology of Sex Determination. John Wiley & Sons, Ltd, 2008. http://dx.doi.org/10.1002/0470868732.ch17.
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Janes, Daniel E. "Extinct and Extant Reptiles: A Model System for the Study of Sex Chromosome Evolution." In Evolutionary Biology – Concepts, Molecular and Morphological Evolution. Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-12340-5_1.
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Sherratt, Thomas N., and David M. Wilkinson. "Why Sex?" In Big Questions in Ecology and Evolution. Oxford University Press, 2009. http://dx.doi.org/10.1093/oso/9780199548606.003.0006.
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There is considerable confusion about the meaning of sex. It can be taken to mean gender (male or female), a form of recreation (‘hot sex’), or a form of procreation (‘sexual reproduction’). To most biologists, sex is none of the above. Instead, one definition of sex would simply be a process that combines genetic material from more than one individual. By this definition, sex is not in itself reproduction. For one thing, reproduction is not a necessary consequence of sex (many bacteria can simply share DNA through hooking up via conjugation), and sex is not always needed for reproduction (dandelions, greenfly, and starfish, to name a few, can all produce viable offspring without it). In fact, the specific act of combining genetic material can be thought of as the precise opposite of reproduction since it typically involves the coming together of the genetic material of two cells (‘gametes’) to create one (‘zygote’), rather than the splitting of one cell into two. All that said, in eukaryotic species (like us, with chromosomes housed discretely within a nuclear membrane) sex is a precursor to reproduction. Indeed, in some species including humans, other mammals, and many insect species, sex is an essential step in the production of offspring. To understand what sex is, we must first cover some basic genetics. Let us begin by thinking about the process of combining two gametes to produce a zygote—a fertilized egg. Naturally, if you simply combine all of the genetic material present in the nucleus of one of your typical cells with that derived from some lucky mate, then any resultant zygote would contain double the number of chromosomes. For example, humans are diploid, and have 23 pairs of chromosomes (one chromosome from each pair derived from each parent). Therefore, if you simply combine chromosomes from the diploid cells of two potential human parents, then the resulting zygote would have 46 pairs of chromosomes, and if two such individuals mated then their offspring would have 92 pairs of chromosomes. Clearly such accumulation of genetic material would quickly get out of hand, and cells would rapidly become obese with chromosomes.
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Beukeboom, Leo W., and Nicolas Perrin. "The evolution of sex chromosomes." In The Evolution of Sex Determination. Oxford University Press, 2014. http://dx.doi.org/10.1093/acprof:oso/9780199657148.003.0005.
Full textConference papers on the topic "Sex chromosomes Evolution"
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Gorelick, Root, and Roy Osborne. "Evolution of Dioecy and Sex Chromosomes in Cycads." In CYCAD 2005. The New York Botanical Garden Press, 2007. http://dx.doi.org/10.21135/893274900.020.
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"Composition of sex chromosomes of veiled chameleon (Chamaeleo calyptratus, Iguania, Squamata) reveals new insights into sex chromosome evolution of iguanian lizards." In Bioinformatics of Genome Regulation and Structure/Systems Biology (BGRS/SB-2022) :. Institute of Cytology and Genetics, the Siberian Branch of the Russian Academy of Sciences, 2022. http://dx.doi.org/10.18699/sbb-2022-097.
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Cordaux, Richard. "Evolution of new sex chromosomes by lateral genome transfer of bacterial symbiont in pillbug." In 2016 International Congress of Entomology. Entomological Society of America, 2016. http://dx.doi.org/10.1603/ice.2016.94155.
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Salimpour, Saeideh, and Ahmed Azab. "A Dynamic Programming Approach to Solve the Facility Layout Problem for Reconfigurable Manufacturing." In ASME 2021 16th International Manufacturing Science and Engineering Conference. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/msec2021-60408.
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Abstract Preparing manufacturing systems to deal with disruptions caused by unexpected factors such as COVID-19 is critical to remain in today’s competitive market. Reconfigurable manufacturing systems (RMS) which are characterized by being rapid and cost-effective in response to market changes, are a good alternative to cope with such unexpected events. From the layout point of view, in an RMS, the layout of facilities needs to be changeable and able to be redesigned easily. Dynamic facility layout problem (DFLP) is a good approach to develop layouts that are capable to be changed and redesigned. Dynamic programming (DP) has been known as one of the effective methods to deal with DFLP. To optimize DFLP by DP, the set of possible layouts for every single period which is called the state-space is given to DP and the best multi-period layout is found. Since the number of possible layouts increases rapidly with the increase in the number of facilities, considering all these layouts encounters two major difficulties, memory requirements and computer time requirements. This paper proposes a method that has two main phases. In the first phase, the set of layouts to be considered in each period are determined using a heuristic approach. These layouts are the states in the DP approach where the periods constituted the decomposition stages. The recursive formulation of DP is solved in the second phase using a hybridized metaheuristic approach. The proposed approach restricts the DP to a good subset of the state-space. A genetic algorithm is applied to search for the best subset of layouts where each chromosome represents one subset of layouts. This subset is given to DP to be solved and the result is considered as the fitness of the chromosome. By the evolution of the chromosomes, the best subset of layouts that leads to the best multi-period layout plan is found. The proposed approach is evaluated against DP benchmarks in the literature. Computational results show that the proposed approach is able to provide more efficient solutions, especially for large-sized problems.
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Mouhadjer, Hassan, M. Mansour, M. Ouslim, and B. Bouchiba. "Segmentation of human chromosome images using distance regularized level set evolution." In 2013 2nd International Conference on Advances in Biomedical Engineering (ICABME). IEEE, 2013. http://dx.doi.org/10.1109/icabme.2013.6648886.
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Giannelli, B. F. "MOLECULAR GENETICS OF HAEMOPHILIA." In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1643981.
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Haemophilia B, an X-linked recessive disease with an incidence of 1/30,000 newborn males, is due to defects in the gene for coagulation factor IX, which is on the long am of the X chromosome at band Xq27.1. This gene consists of approximately 34 Kb and contains 8 exons which specify a mRtfc of 2803 residues coding for a protein of 415 aa preceded by a prepro signal peptide of 46 aa. Coripanson of the functional domains of the factor IX protein with the exon structure of the gene supports the exon/protein domain hypothesis of gene evolution. The factor IX gene seems to be formed by a number of functionally and evolutionally independent modules. The signal peptide and the gla (γcarboxy-glutamic) region encoded in the first three exons are homologous to those of factor X, protein C and prothrombin. Thevfourth and fifth exons which code for the connecting peptide are homologous to one another and to the epidermal growth factor, a module that has been used in the construction of a great variety of proteins including different members of the coagulation and fibrinolytic pathways. The sixth exon encodes the activation peptide region, while the catalytic region of factor IX is coded by the seventh and eighth exon. This is at variance with other serine protease genes that have different exons for the segments containing the cardinal ami no-acids of the active centre (histidine, aspartic acid and serine).Natural selection acts against detrimental mutations of the factor IX gene and at each generation a proportion of haemophilia B genes is eliminated, as a significant number of patients does not reproduce. There appears to be no selective advantage to the heterozygote and therefore haemophilia B is maintained in the population by new mutations. Consequently, a significant proportion of patients should be born to non-carrier mothers, and unrelated patients should carry different gene defects, as recently verified by detailed analysis of individual haemophilia B genes.The defects of factor IX described so far comprise both point mutations and gene deletions. The latter affect either part or the whole of the gene and are often associated with the development of antibodies against therapeutically adninistered factor IX (the inhibitor complication). Since gene deletions may result in the complete absenceof factor IX synthesis or in the production of an extremely abnormal product, it has been suggested that mutationspreventing the synthesis of a factor IX gene product capable of inducing immune tolerance to normal factor IX is important in predisposing to the inhibitor complication.Among the point mutations described so far, those affecting the signal peptide are of particular interest. Substitutions of the arginine at positions -4 and -1 cause failure of propeptide cleavage. Thus they indicate that the propeptide consists of 18 aa an(lthat lts excision is necessary for factor IX function. It appears also that the propeptide contains a signal for γcarboxylation which has been conserved during the evolution of different γcarboxylated proteins.In spite of coagulant treatment, haemophilia B is a serious disease and one for which genetic counselling is required. Paramount for this is the detection of carriers and the diagnosis ofaffected male fetuses. DNA probes derived from the cloned factor IX gene have been used for this purpose. Carrier and first or second trimester prenatal diagnoses have been done using factors IX gene markers to follow the transmission of haemophilia B genes. Six sequence variations causing restriction fragment length polymorphisms (RFLP) in the factor IX gene have been detected and used as markers for such indirect diagnoses The efficiency of the above markers is reduced by linkage disequilibrium but, nevertheless, they offer definite carrier and nremtal diagnoses in 75-80% of the relatives of familial cases of haemophilia B.The indirect detection of gene defects is of modest help in the counselling of individuals from the families of isolated patients, but new methods for the direct detection of gene mutations promise better results in such families and also the attainment of % diagnostic success in relatives of familial cases.Finally the successful expression of recombinant factor IX genes in tissue culture and transgenic mammals raises hopes of therapeutic advances.
Reports on the topic "Sex chromosomes Evolution"
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Hulata, Gideon, Thomas D. Kocher, and Micha Ron. Elucidating the molecular pathway of sex determination in cultured Tilapias and use of genetic markers for creating monosex populations. United States Department of Agriculture, 2007. http://dx.doi.org/10.32747/2007.7695855.bard.
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The objectives of this project were to: 1) Identify genetic markers linked to sex-determining genes in various experimental and commercial stocks of O. niloticusand O. aureus, as well as red tilapias; 2) Develop additional markers tightly linked to these sex determiners, and develop practical, non-destructive genetic tests for identifying genotypic sex in young tilapia; A third aim, to map sex modifier loci, was removed during budget negotiations at the start of the project. Background to the topic. A major obstacle to profitable farming of tilapia is the tendency of females to reproduce at a small size during the production cycle, diverting feed and other resources to a large population of small, unmarketable fish. Several approaches for producing all-male fingerlings have been tried, including interspecific hybridization, hormonal masculinization, and the use of YY-supermale broodstock. Each method has disadvantages that could be overcome with a better understanding of the genetic basis of sex determination in tilapia. The lack of sex-linked markers has been a major impediment in research and development of efficient monosex populations for tilapia culture. Major conclusions, solutions, achievements. We identified DNA markers linked to sex determining genes in six closely related species of tilapiine fishes. The mode of sex determination differed among species. In Oreochromis karongaeand Tilapia mariaethe sex-determining locus is on linkage group (LG) 3 and the female is heterogametic (WZ-ZZ system). In O. niloticusand T. zilliithe sex-determining locus is on LG1 and the male is heterogametic (XX-XY system). We have nearly identified the series of BAC clones that completely span the region. A more complex pattern was observed in O. aureus and O. mossambicus, in which markers on both LG1 and LG3 were associated with sex. We found evidence for sex-linked lethal effects on LG1, as well as interactions between loci in the two linkage groups. Comparison of genetic and physical maps demonstrated a broad region of recombination suppression harboring the sex-determining locus on LG3. We also mapped 29 genes that are considered putative regulators of sex determination. Amhand Dmrta2 mapped to separate QTL for sex determination on LG23. The other 27 genes mapped to various linkage groups, but none of them mapped to QTL for sex determination, so they were excluded as candidates for sex determination in these tilapia species. Implications, both scientific and agricultural. Phylogenetic analysis suggests that at least two transitions in the mode of sex determination have occurred in the evolution of tilapia species. This variation makes tilapias an excellent model system for studying the evolution of sex chromosomes in vertebrates. The genetic markers we have identified on LG1 in O. niloticusaccurately diagnose the phenotypic sex and are being used to develop monosex populations of tilapia, and eliminate the tedious steps of progeny testing to verify the genetic sex of broodstock animals.
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Tel-Zur, Neomi, and Jeffrey J. Doyle. Role of Polyploidy in Vine Cacti Speciation and Crop Domestication. United States Department of Agriculture, 2012. http://dx.doi.org/10.32747/2012.7697110.bard.
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1. Abstract: Over the past 25 years, vine cacti of the genera Hylocereus and Selenicereus have been introduced into Israel and southern California as new exotic fruit crops. The importance of these crops lies in their high water use efficiency and horticultural potential as exotic fruit crops. Our collaboration focused on the cytological, molecular and evolutionary aspects of vine cacti polyploidization to confront the agricultural challenge of genetic improvement, ultimately to improve success of vine cacti as commercial fruit crop plants. More specifically, we worked on the: 1- Identification of the putative ancestor(s) of the tetraploid H. megalanthus; 2- Determination of the number of origins of H. megalanthus (single vs. multiple origins of polyploidy); 3- Cytogenetic analysis of BC1 and F1 hybrids; 4- Determination of important agricultural traits and the selection of superior hybrids for cultivation. The plant material used in this study comprised interspecific Hylocereus F1 and first backcross (BC1) hybrids, nine Hylocereus species (58 genotypes), nine Selenicereus species (14 genotypes), and four Epiphyllum genotypes. Two BC1 hexaploids (BC-023 and BC-031) were obtained, a high ploidy level that can be explained only by a fertilization event between one unreduced female gamete from the triploid hybrid and a balanced gamete from the pollen donor, the diploid H. monacanthus. These findings are scientific evidence that support the possibility that “hybridization followed by chromosome doubling” could also occur in nature. Cytomixis, the migration of chromatin between adjacent cells through connecting cytoplasmatic channels, was observed in vine cacti hybrids and may thus imply selective DNA elimination in response to the allopolyploidization process. Evidence from plastid and nrDNA internal transcribed spacers (ITS) sequences support the placement of H. megalanthus within a monophyletic Hylocereus group. Furthermore, both plastid and ITS datasets are most consistent with a conclusion that this tetraploid species is an autopolyploid, despite observations that the species appears to be morphologically intermediate between Hylocereus and Selenicereus. Although the possibility of very narrow allopolyploidly (i.e., derivation from parents that are barely diverged from each other such as closely related species in the same genus) cannot be ruled out entirely based on our data (in part due to the unavailability of Hylocereus species considered to be morphologically the closest relatives of H. megalanthus), the possibility of H. megalanthus representing an intergeneric cross (i.e., Hylocereus × Selenicereus) seems extremely unlikely. Interestingly, the process of homogenization of ITS sequences (concerted evolution) is either incomplete or lacking in both Hylocereus and Selenicereus, and the inclusion of several artificial hybrids in the molecular study revealed the potential for biparental plastid inheritance in Hylocereus. The most important agricultural implication of this research project was the information collected for F1 and BC1 hybrids. Specifically, this project concluded with the selection of four superior hybrids in terms of fruit quality and potential yields under extreme high temperatures. These selected hybrids are self-compatible, avoiding the need for hand cross pollination to set fruits, thus reducing manpower costs. We recently offered these hybrids to growers in Israel for prioritized rapid evaluation and characterization.