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In most cases, these remnants remain inactive, but recently scientists have discovered they sometimes take on surprising roles in developing embryos and may even push mammalian evolution.
Researchers found that the virus active in the mouse genome that influences sex ratios is relatively recent — in evolutionary terms — and is enriched on the X chromosome.
The sex of human and all mammalian babies may be determined by a simple modification of a virus that insinuated itself into the mammalian genome as recently as 1.5 million years ago, a new Yale University-led study has found.“Basically, these viruses appear to allow the mammalian genome to continuously evolve, but they can also bring instability,” said Andrew Xiao of the Department of Genetics and Yale Stem Cell Center, senior author of the paper published online March 30 in the journal Nature.
“Aside from the embryo, the only other places people have found this virus active is in tumors and neurons.”Xiao and the Yale team discovered a novel mechanism by which the early embryo turns off this virus on the X chromosome, which ultimately determines the sex of an organism.
Xiao estimated that more than 40% of the human genome is made up of such remnants of viral duplications.Epigenetics modulates gene expression during development without actually altering the sequences of genes.In the new marker, a methyl bond is added to adenine — one of the four nucleotides that comprise base pairs in DNA — allowing it to silence genes.The Yale-led team found the mechanism that disables the virus.
The newly discovered modification in mammals is a surprising expansion of the epigenetic toolbox, say the researchers.At this stage, it can cause serious damage to the body but can still be treated Treatment for syphilis is usually a course of antibiotics.