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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.
It is possible on rare occasions for ploidy to increase in the germline, which can result in polyploid offspring and ultimately polyploid species. This is an important evolutionary mechanism in both plants and animals and is known as a primary driver of speciation . [ 8 ]
The main goals of diploidization are: (1) To ensure proper gene dosage; and (2) to maintain stable cellular division processes. This process does not need to occur rapidly for all chromosomes in one or few steps. In recent polyploid events, segments of the genome may still remain in a tetraploid status.
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]
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.
In these polyploid unisexual females, an extra premeiotic endomitotic replication of the genome, doubles the number of chromosomes. [46] As a result, the mature eggs that are produced subsequent to the two meiotic divisions have the same ploidy as the somatic cells of the adult female salamander.
Diploid and polyploid cells whose chromosomes have the same allele at a given locus are called homozygous with respect to that locus, while those that have different alleles at a given locus are called heterozygous. [3] The ordered list of loci known for a particular genome is called a gene map.
Thus, paleopolyploidy is identified as a "peak" on the duplicate number vs. Ks graph (shown on the right). However, using Ks plots to identify and document ancient polyploid events can be problematic, as the method fails to identify genome duplications that were followed by massive gene elimination and genome refinement.