Auswahl der wissenschaftlichen Literatur zum Thema „Genotype 1. eng“

Bones are multifunctional passive organs of movement that supports soft tissue and directly attached muscles. They also protect internal organs and are a reserve of calcium, phosphorus and magnesium. Each bone is covered with periosteum, and the adjacent bone surfaces are covered by articular cartilage. Histologically, the bone is an organ composed of many different tissues. The main component is bone tissue (cortical and spongy) composed of a set of bone cells and intercellular substance (mineral and organic), it also contains fat, hematopoietic (bone marrow) and cartilaginous tissue. Bones a

Phenotypic plasticity is the property of a genotype to produce different phenotypes in response to different environmental conditions (Bradshaw 1965; Mazer and Damuth, this volume, chapter 2). Simply put, students of phenotypic plasticity deal with the way nature (genes) and nurture (environment) interact to yield the anatomy, morphology, and behavior of living organisms. Of course, not all genotypes respond differentially to changes in the environment, and not all environmental changes elicit a different phenotype given a particular genotype. Furthermore, while the distinction between genotype and phenotype is in principle very clear, several complicating factors immediately ensue. For example, the genotype can be modified by environmental action, as in the case of DNA methylation patterns (e.g., Sano et al. 1990; Mazer and Damuth, this volume, chapter 2). More intuitively, since environments are constantly changed by the organisms that live in them, the genetic constitution of a population influences the environment itself. Perhaps the most intuitive way to visualize phenotypic plasticity is through what is termed a norm of reaction. This genotype-specific function relates the phenotypes produced to the environments in which they are produced. The figure presents a simple example with a population made of three different genotypes experiencing a series of environmental conditions. Genotype 1 yields a low phenotypic value toward the left end of the environmental continuum (say, an insect with small wings at low temperature) but a high phenotypic value at the opposite environmental extreme (say, large wings at high temperature). Genotype 3, however, does the exact opposite, while genotype 2 is unresponsive to environmental changes, always producing the same phenotype regardless of the conditions (within the range of environments considered). Even though the case presented in figure 5.1 is very simple (notice, for example, that the reaction norms are linear, which is unlikely in real situations), several general principles are readily understood following a closer analysis: . . . 1. Let us consider the relationship between phenotypic plasticity and reaction norms. While the two terms are often used as synonyms, they are clearly not. A reaction norm is the trajectory in environment- phenotype space that is typical of a given genotype; plasticity is the degree to which that reaction norm deviates from a flat line parallel to the environmental axis. . . .

The thrifty genotype proposes that populations susceptible to CVD and DM₂ have been subjected to intermittent, serious food shortages and have evolved to cope, e.g. through insulin resistance. This means their glucose is not readily entering the muscle to be used there but is preferentially used by the brain and liver. Glucose is converted to fat in the liver and stored for times of food scarcity. This thrifty state is not, however, beneficial in modern times where food is plentiful. This hypothesis remains a common explanation, including for South Asians’ susceptibility to DM₂. The hypothesis has lost support, mostly because of lack of confirmatory empirical data, but has sparked-off new ideas, e.g. the mitochondrial efficiency hypothesis as an adaptation to climatic change, and the predation release hypothesis which sees diminishing need for leanness and agility as triggering higher obesity prevalence. These newer ideas need more research.

Narcolepsy is the specific syndrome of daytime sleepiness with cataplexy, where there is a sudden loss of muscle tone—often provoked by the anticipation of emotions—leading to a tendency to fall, mouth opening, dysarthria or mutism, and facial muscle jerking. It is associated with loss of hypocretin (orexin) neurons in the hypothalamus, hypocretin-1 concentrations in the cerebrospinal fluid below 100 ng/litre, and the HLA genotype DQ B1*0602. Once established, narcolepsy is lifelong; spontaneous recovery does not occur. Treatment—which is essential to restore school performance, work, driving ability and quality of life—is with stimulant (e.g. amphetamine) and anticataplectic (e.g. clomipramine) drugs, supported by a 15-min nap once or twice a day....

Behavior, like other phenotypic traits, varies as a function of genes and environment. Variation occurs at all demographic levels, within individuals over time, between individuals, and between populations and species. Whether variation is important will depend on the behavior and its context. For example, whether a bird scratches its head by extending a leg above or below the adjacent wing may not have profound fitness consequences, although species differences in this character may shed light on phylogenetic relationships (e.g., Wallace 1963; Simmons 1964). In contrast, other behaviors, such as the instantaneous decision to migrate or not, may affect fitness directly by altering the schedule of fecundity or mortality (Dingle et al. 1982). Such strategic behaviors (Maynard Smith 1982), which often depend for their expression on the assessment of local cues (Moran 1992), are complicated and important evolutionary traits. The phenotypic variability that defines them, however, has hindered our ability to treat them with formal evolutionary–genetic analyses that are central to the complete understanding of any putative adaptation. Much of the evolutionarily important variation observed in strategic behavior probably stems from differences among individuals due to genotype–environment interactions. To illustrate this in the most general terms, consider that behavioral distinctions among individuals may be based on (1) differences in the environmental conditions they experience, (2) differences in genetic elements that code for specific tactics or predispositions, or (3) differences in the genotype–environment interaction, manifested through developmental or facultative pathways, that is, “norms of reaction” (Schmalhausen 1949). Norms of reaction are functions that describe how a genotype is translated into a phenotype by the environment. They are becoming widely employed as a paradigm in evolutionary studies of physiological and life-history traits (e.g., Dingle 1992; reviewed by Stearns 1989), but are not yet used widely in studies of behavioral traits (but see Thompson this volume). Because much of the variation that behaviorists observe within populations and species is likely the result of a complex combination of individual differences in genetic code and differences in environment, norms of reaction need to be explored as a method for understanding the sources and structure of behavioral variation.

Arrhythmogenic cardiomyopathy (AC) is a rare non-ischaemic cardiomyopathy with a prevalence in of 1:200 to 1:5000. In the 1980s, the disorder was demonstrated to be a major cause of sudden death (SD) in the young and athletes, thus emphasizing the need for early diagnosis for disqualification from sport activity. Pre-participation screening using ECG is effective in detecting ECG abnormalities which raise suspicion of the disease, requiring additional second- and third-level investigations to obtain a definite diagnosis. Cardiac magnetic resonance (CMR), which can detect both morpho-functional and tissue abnormalities, is probably the best tool for assessing doubtful cases. The rarer left ventricular variant (‘non-ischaemic left ventricular scar’) is not detected by ECG at first-level pre-participation screening, which presents a major challenge for SD prevention. Risk stratification consensus criteria recommend use of an implantable cardioverter defibrillator (ICD). Use of pre-participation screening and automated external defibrillators (AEDs), working together should help to prevent SD. Since at least 60% of cases are heredofamilial and usually present desmosome gene mutations, genetic investigation should be carried out in the proband and cascade genetic screening should be offered to first-degree family members for primary prevention. Basic research into the AC pathogenic mechanisms is in progress, and there is clinical and experimental evidence that exercise with right ventricular overload may favour onset and progression of AC, at least in genotype-positive patients. Reduction of sports activity will not only prevent abrupt onset of ventricular arrhythmias with the risk of SD, but may also delay phenotype expression.

Down syndrome (DS) is the most common genetic cause of significant intellectual disability in humans. It was one of the first chromosomal disorders of humans to be associated with intellectual disabilities and, as such, has provided an evidence-based foundation from which work on many different disorders has been launched. John Langdon Down first described this syndrome in 1866 using the term mongoloid idiocy. The initial clinical description of DS comprised physical features (e.g., epicanthal folds, flat and broad face, enlarged tongue, microcephaly, short stature) and cognitive characteristics (e.g., intellectual impairment, fine and gross motor coordination problems, poor speech articulation). He also described a relatively positive personality in these individuals. Contemporary topographical descriptions are remarkably similar to Down’s description nearly 150 years ago, but a variety of other healthrelated issues have been uncovered since that time including congenital cardiac abnormalities, hypotonia, hearing and visual impairments, hypothyroidism, and precocious aging (Rasmussen, Whitehead, Collier, and Frias 2008). In accordance with the core tenets of this text, in this chapter we discuss epidemiology, etiology, and what is known about core pathophysiological mechanisms in DS; neurological abnormalities, including contemporary findings in neuroimaging; neurocognitive and socialbehavioral manifestations; and emergent evidencebased treatment efforts. The chapter concludes with a brief discussion of the phenotype-genotype linkages for DS, and a review of the priorities set by a national panel of experts in DS (Rasmussen et al. 2008). When compared to other congenital abnormalities, DS represents one of the most common disorders. Contemporary prevalence estimates indicate the occurrence of DS in approximately 9.0–11.8 (Shin et al. 2009) to 13.66 (Canfield et al. 2006) per 10,000 live births. The rate of infants born with DS also has a strong relationship with increasing maternal age. For example, a 20-year-old mother has a 1 in 1,923 chance of giving birth to an infant with Down syndrome, whereas the chance for a 49-year-old mother is 1 in 12 (Prescott 1988). The cause of this phenomenon, however, is not well understood (Lamb and Hassold 2004).

<em>Abstract</em>.—Shoal bass <em>Micropterus cataractae</em> are endemic to the Apalachicola drainage, including the Chattahoochee (Alabama and Georgia), Flint (Georgia), and Chipola (Florida) River systems. Habitat modification, including extensive dam construction, has reduced population sizes in many areas of their native range and, in some cases, has led to local population extinctions. The most abundant Shoal Bass populations reside in the Flint River, but even there they are suspected to be hybridizing with the invasive Spotted Bass <em>M. punctulatus</em>, which have become established in the system. To assess the threat that hybridization poses to the genetic integrity of Shoal Bass in the Flint River, tissue samples were collected from presumptive Shoal Bass, nonnative congeners, and their potential hybrids. Fish were collected from multiple locations above and below the Flint River Dam and from Ichawaynochaway Creek, a southern tributary. These were genotyped using 17 polymorphic microsatellite loci and a subset was sequenced for the mitochondrial DNA (mtDNA) 16S ribosomal RNA gene. Above the Flint River Dam, 12% of the specimens carried nonnative alleles; however, genomic proportions of these alleles were low (1%). Below the Flint River Dam, the percentage of hybrid specimens ranged from 17% to 43% and sample genomic proportions increased to 6–7%. In Ichawaynochaway Creek, the percentage of hybrid specimens was 27% and the sample genomic proportion was 7%. Pure spotted bass were collected below the Flint River Dam; most F<sub>1</sub> hybrids were collected in Ichawaynochaway Creek. The mtDNA of hybrids indicated that Shoal Bass males cross with Spotted Bass females more frequently than the converse. Hybridization was bidirectional (i.e., hybrids were found to backcross to both Spotted Bass and Shoal Bass). Because introgressive hybridization occurs, the flux of nonnative alleles in this system should be monitored and all broodfish in stocking programs should be screened. Studies should be implemented to determine if natural genetic mechanisms (e.g., disruptive selection) will be sufficient to maintain the integrity of the species boundaries.