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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.
Organisms in which a particular chromosome, or chromosome segment, is under- or over-represented are said to be aneuploid (from the Greek words meaning "not", "good", and "fold"). Aneuploidy refers to a numerical change in part of the chromosome set, whereas polyploidy refers to a numerical change in the whole set of chromosomes. [44]
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).
This was previously thought to be the highest chromosome number known for a mammal, [3] but it has since been found that the plains viscacha rat or red viscacha rat (Tympanoctomys barrerae) has 4x = 2n = 102. [4]
Przewalski's horse has the highest diploid chromosome number among all equine species. They can interbreed with the domestic horse and produce fertile offspring, with 65 chromosomes. [6] The mitochondrial genome has 37 genes that are 99.63% identical to that of the domestic horse. [25]
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.
[1] [2] By analysing the similarities and differences in the chromosomes, karyotype evolution and species evolution can be reconstructed. The number, structure, and behaviour of chromosomes is of great value in taxonomy , with chromosome number being the most widely used and quoted character.
The doubling of its chromosome number was presumably by errors in mitosis or meiosis within the animal's reproductive organs. [15] A comparison of the chromosomes of the plains viscacha rat and the mountain viscacha rat suggested that the chromosomes of the plains viscacha rat increased relatively rapidly (in evolutionary terms) due to a ...