Millions of years ago, one species of frog diverged into two species. Millions of years later, the two frogs became one again, but with a few extra chromosomes due to whole genome duplication. Such is the curious case of the African clawed frog, Xenopus laevis, a frog whose genome contains nearly double the number of chromosomes as the related Western clawed frog, Xenopus tropical is.
In the evolution of species, different events have occurred over millions of years that have increased the number of chromosomes in some organisms. Polyploidy describes an event that increases the number of copies of each chromosome. Vertebrates have undergone at least two different polyploidy events since their original divergence. While it is relatively rare nowadays to observe a mammal, reptile or bird with an abnormal number of chromosomes, polyploidy is common in fish, amphibians and plants.Paper. (paywall) – Adam M. Session et al., Genome evolution in the allotetraploid frog Xenopus laevis. Nature, 2016; 538 (7625): 336 DOI: 10.1038/nature19840More.
See also: New species originated via polyploidy?
Genome doubling (polyploidy) a key factor in evolution?
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