Scientists have decoded the DNA of an animal who has lived without sex for 18 million years

© Photo : Karin Kiontke and David FitchЧервь Diploscapter pachys, reproducing exclusively asexuallyScientists have decoded the DNA of an animal who has lived without sex for 18 million years© Photo : Karin Kiontke and David Fitch

. Genetics from the United States for the first time decoded the genome of the worm Diploscapter pachys, reproducing exclusively asexually for 18 million years, and found out why he still became a victim of evolution, says the article, published in the journal Current Biology.

«Scientists have long been trying to understand how such animals do exist for many million years without sex. The very fact of their survival is contrary to our ideas about the role that sex plays in getting rid of mutations and adaptation to the new environment,» says David Fitch (David Fitch), a geneticist from the University of new York (USA).

The first multicellular animals that appeared on Earth about 550 million years ago, was originally breed asexually, but then they quickly switched to sexual reproduction by exchanging genetic material and combining it.

The reason for this, according to the supporters of the so-called «red Queen hypothesis» was the parasites and viruses that can evolve faster than their sexless victims. As shown by recent experiments with crustaceans-Daphnia, are able to reproduce both by asexual reproduction prolonged significantly reduces their resistance to infection and denying them protection from parasites.

As noted by Fitch, worms of Diploscapter pachys, as well as some rotifers and crustaceans, are the only exception to this rule – these creatures have lived for millions of years without sex and not become extinct. The secret to their survival is one of the most interesting evolutionary puzzles, and scientists have only now been able to solve it, deciphering the DNA of these worms.

Almost immediately, biologists noticed an unusual thing – the whole genome of these nematodes was «glued» into one giant pair of chromosomes that is not typical for his nearest relative, Caenorhabditis elegans has six pairs of chromosomes, and other worms. What is even more interesting, almost all of the genes in these chromosomes remained in their seats and not moved for 18 million years of separate evolution of these creatures.

This is an unusual property of DNA Diploscapter pachys is the product of another evolutionary «innovation» is the lack of worms in the DNA of genes that control the first stage of meiosis. This word scientists understand a key part of the process of division of germ cells, when chromosomes are «mixed» up and «taken away» two pairs future eggs or sperm.

Due to this, the genome of these worms is retained high genetic diversity – the division of the chromosomes occurs and they retain the view that they inherited from their ancestors, yet reproduce sexually. Accordingly, the descendants of Diploscapter pachys keep two sets of very different genes, the differences between them, as scholars have noted, roughly comparable to those characteristic of animals, producing offspring sexually.

«I think we’ve solved the riddle — worms Diploscapter pachys managed to get rid of the main drawback of asexual reproduction, maintaining high genetic diversity, and protecting yourself from the accumulation of recessive mutations. Extremely ironic is that nematodes have achieved this, breaking the mechanism that prevents their appearance in sexual reproduction», concludes Fitch.

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