Academic literature on the topic 'Chromosom W'

Genetics is the study of heredity. Each individual’s makeup, or phenotype, is determined by nature and modified by environmental factors. DNA identity analysis is based strictly on heredity, and only in the rare case where a human had a bone marrow transplant would the white blood cell genotype differ from that inherited. Difficulties can arise with specimens because of DNA degradation or contamination by extraneous materials, and mixed cell populations could be present in tumorous tissue. The analyst must always be cognizant of these complicating factors. The concept of the gene was advanced by the Moravian monk Gregor Mendel in 1865 based on observations he made after crossing different varieties of garden peas; these experiments are considered the beginning of the discipline of genetics. (The term gene was actually coined by the Danish plant scientist W. Johannsen in the early 1900s.) Mendel formulated two laws. The law of segregation or separation states that two members of each gene pair (alleles) in a diploid organism separate to different gametes during sex cell formation. The law of independent assortment states that members of different pairs of alleles, if located on separate chromosomes or far apart on the same homologous chromosome pair, assort independently into gametes. These laws are basic to the understanding of biological family relationships and play a critical role in such contemporary issues as paternity testing and immigration disputes. The basic unit of life is the cell. Cells are microfactories in which raw materials (amino acids, simple carbohydrates, lipids, and trace elements) are received, new substances (proteins, complex lipids, carbohydrates, and nucleic acids) are produced, and wastes are removed. The thousands of different enzymes required for the myriad ongoing chemical reactions are key to the efficient functioning of cells. Each cell has the ability to self-replicate using the deoxyribonucleic acid (DNA) code as the blueprint, raw materials as building blocks, and enzymes as catalysts. It has been estimated that the average human being is composed of approximately 100 trillion cells—a considerable amount of DNA.