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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.
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.
When a human germ cell undergoes meiosis, the diploid 46 chromosome complement is split in half to form haploid gametes. After fusion of a male and a female gamete (each containing 1 set of 23 chromosomes) during fertilization, the resulting zygote again has the full complement of 46 chromosomes: 2 sets of 23 chromosomes.
The ZW sex-determination system is a chromosomal system that determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects (including butterflies and moths), the schistosome family of flatworms, and some reptiles, e.g. majority of snakes, lacertid lizards and monitors, including Komodo dragons.
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.
Chromosomes line up in the middle of the cell by microtubule organizing centers (MTOCs) pushing and pulling on centromeres of both chromatids thereby causing the chromosome to move to the center. At this point the chromosomes are still condensing and are currently one step away from being the most coiled and condensed they will be, and the ...
Possessing chromosomes of varying shapes is generally the result of a chromosomal translocation or chromosomal inversion. In a translocation, genetic material is transferred from one chromosome to another, either symmetrically or asymmetrically (a Robertsonian translocation). In an inversion, a segment of a chromosome is flipped end-for-end.
The sister chromatids by convention are now called sister chromosomes as they move toward opposing poles. [30] The process ends with telophase II, which is similar to telophase I, and is marked by decondensation and lengthening of the chromosomes and the disassembly of the spindle. Nuclear envelopes re-form and cleavage or cell plate formation ...