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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 .
Aldabrachelys gigantea, Aldabra giant tortoise (2019 draft, [219] 2022 chromosome scale [220]) † Chelonoidis abingdonii, Pinta Island giant tortoise (2019 [219]) Chelonoidis phantasticus, Fernandina Island Galapagos giant tortoise (2022 [221])
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.
Euploidy and aneuploidy describe having a number of chromosomes that is an exact multiple of the number of chromosomes in a normal gamete; and having any other number, respectively. For example, a person with Turner syndrome may be missing one sex chromosome (X or Y), resulting in a (45,X) karyotype instead of the usual (46,XX) or (46,XY).
Some animal and plant species are polyploid [Xn], having more than two sets of homologous chromosomes. Important crops such as tobacco or wheat are often polyploid, compared to their ancestral species. Wheat has a haploid number of seven chromosomes, still seen in some cultivars as well as the wild progenitors. The more common types of pasta ...
A comparative chromosome map of birds' and mammals' inferred human homologies (right numbers) on chromosome idiograms [29] The third step occurred when molecular techniques were incorporated into cytogenetics. These techniques use DNA probes of diverse sizes to compare chromosomes at the DNA level.
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.
Further, nearly half of the chromosomes in the horse genome show conserved synteny with a human chromosome, far more than between dogs and humans. [2] This is a high degree of conserved synteny and may help researchers use insights from one species to illuminate the other.