The bull Y chromosome has evolved to bully its way into gametes

Scientists present the first ever full, high-resolution sequence of the Y chromosome of a Hereford bull. The research, more than a decade in the making, suggests that bulls' Y chromosomes have evolved dozens of copies of the same genes in a selfish attempt to make more males -- a move that is countered in the female-determining X chromosome.

source https://www.sciencedaily.com/releases/2020/11/201118141636.htm