Another change in neo-X that Bachtrog suspects is taking place is the elimination of genes that are harmful to females. Biologists have realized recently that some genes have opposite effects in males and females, and evolution is a tug of war between males jettisoning genes that they find detrimental only to have females put them back, and vice versa.
"A good place to put sexually antagonistic genes that are beneficial to one sex but detrimental to the other is on the sex chromosomes," she said. The Y always ends up in the male, she said, so genes on the Y chromosome won't affect females.
"Conversely, the X chromosome becomes feminized with genes that are good for the female but detrimental to the male," said Bachtrog, adding that the X also becomes demasculinized, losing genes that are of use only in the male.
Via Science Daily.