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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]
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.
All great apes have similar genetic chromosome structure. Humans have one pair fewer chromosomes than other apes, as humans have 23 chromosome pairs, while all other apes have 24, [13] with ape chromosomes 12 and 13 fused in the human genome into a large chromosome (which contains remnants of the centromere and telomeres of the ancestral 12 and ...
Number of chromosomes Number of genes predicted Organization Year of completion Arabidopsis thaliana Ecotype:Columbia: Wild mustard Thale Cress Model plant 135 Mb [10] 5 25,498, [11] 27,400, [12] 31,670 (UniProt) Arabidopsis Genome Initiative [13] 2000 [11] Cyanidioschyzon merolae Strain:10D: Red algae: Simple eukaryote: 16.5 Mb 20 5,331 [14]
Trisomy 21 – Down syndrome, an example of a polysomy at chromosome 21 Polysomy is a condition found in many species, including fungi, plants, insects, and mammals, in which an organism has at least one more chromosome than normal, i.e., there may be three or more copies of the chromosome rather than the expected two copies. [1]