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The list of organisms by chromosome count describes ploidy or numbers of chromosomes in the cells of various plants, animals, protists, and other living organisms.This number, along with the visual appearance of the chromosome, is known as the karyotype, [1] [2] [3] and can be found by looking at the chromosomes through a microscope.
The basic number of chromosomes in the somatic cells of an individual or a species is called the somatic number and is designated 2n. In the germ-line (the sex cells) the chromosome number is n (humans: n = 23). [4] [5] p28 Thus, in humans 2n = 46. So, in normal diploid organisms, autosomal chromosomes are present in two copies.
The first step of the Human Genome Project took place when Tjio and Levan, in 1956, reported the accurate diploid number of human chromosomes as 2n = 46. [ 6 ] During this phase, data on the karyotypes of hundreds of mammalian species (including information on diploid numbers, relative length and morphology of chromosomes, presence of B ...
Though polyploidy in humans is not viable, mixoploidy has been found in live adults and children. [45] There are two types: diploid-triploid mixoploidy, in which some cells have 46 chromosomes and some have 69, [46] and diploid-tetraploid mixoploidy, in which some cells have 46 and some have 92 chromosomes. It is a major topic of cytology.
Polyploidy occurs in some tissues of animals that are otherwise diploid, such as human muscle tissues. [45] This is known as endopolyploidy. Species whose cells do not have nuclei, that is, prokaryotes, may be polyploid, as seen in the large bacterium Epulopiscium fishelsoni. [46] Hence ploidy is defined with respect to a cell.
Ploidy/Chromosomes in human DNA copy number/Chromatids in human Process entered by cell Duration spermatogonium (types Ad, Ap and B) germ cells: diploid (2N) / 46: 2C / 46: spermatocytogenesis : 16 days primary spermatocyte: male gametocyte: diploid (2N) / 46: 4C / 2x46: spermatocytogenesis : 24 days secondary spermatocyte: male gametocyte ...
The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms. Most are derived from the amino acid tyrosine. Eumelanin is found in hair, areola, and skin, and the hair colors gray, black, blond, and brown. In humans, it is more abundant in people with dark skin.
In the case of humans, the old centromere went defunct and a more recent form emerged near the modern position of human cen6 (size of 60 Mb). Such cases are known as Evolutionary New Centromeres (ENC). This assembly phenomenon of the human chromosome 6 gives researchers an opportunity to investigate the origin of the ENC on chromosome 6. [4]