Two recent entries in the evolution literature have application to one sex or the other.
Y, chromosome? Because it is a unique structure, the Y chromosome in human males seems more subject to deleterious mutations. The Y is also unable to distribute linked genes through recombination, a process that “makes selection more effective,” the article claimed.
Earlier claims that the Y chromosome is evolving away to extinction were premature. PhysOrg reassures males, “Men can rest easy — sex chromosomes are here to stay,” even though a study from University College London was done on chickens (no epithets, now). Humans have a unique Y chromosome in males, but chickens have a unique W chromosome in females. A research team examined how sex-linked genes on the W chromosome are passed on.
The results confirm that although these chromosomes have shrunk over millions of years, and have lost many of their original genes, those that remain are extremely important in predicting fertility and are, therefore, unlikely to become extinct.
Professor Judith Mank, from the UCL Department of Genetics, Evolution and Environment and senior author said: “Y chromosomes are here to stay, and are not the genetic wasteland that they were once thought to be.”
It was nice of her to rescue the opposite sex. Mank studied sex-linked expression of genes in a variety of chicken breeds and found that they adapt to selection pressures. She deduced that “female-specific selection related to fertility acts to shape the W chromosome, and that the chromosome is able to respond to that selection despite all the problems with the lack of recombination.” To her, this means evolvability is the key to their success:
Professor Mank said: “We have shown that Y and W chromosomes are very important in fertility – the Y in males and the W in females. It is the ability of the W-linked genes to evolve that is the key to their survival, and which suggests that both the Y and the W chromosomes are with us for the long haul.”….
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