They have two X chromosomes. The Y chromosome contains vital genes, for males, that code for things males need. Its really pretty much that. Take away the Y ch

They have two X chromosomes. The Y chromosome contains vital genes, for males, that code for things males need. Its really pretty much that. Take away the Y chromosome and most mammal species aren't going to survive. Even the rats that lost it had the equivalent genes on the X chromosome. The gene expression of females isn't the same as males in short. In spite of the fact that females and males share an X chromosome.