Y Is an Eroded Version of X

I haven't read the referenced paper, but I thought this article on its findings might be of interest to you:

Scientists have cracked the genetic code of the female X chromosome which is linked to more than 300 human diseases and may help to explain why women are so different from men.

It contains 1,100 genes, or about five percent of the human genome, along with information that may help to improve the diagnosis of illnesses ranging from hemophilia, blindness and autism to obesity and leukemia.

The discovery, by an international consortium of scientists, shows that females are far more variable than previously thought and, when it comes to genes, more complex than men.

"The X chromosome is definitely the most extraordinary in the human genome in terms of its inheritance pattern, its unique biology ... and in terms of its association with human disease," said Dr Mark Ross, of the Wellcome Trust Sanger Institute in Britain which led the consortium.

...

The research, which is reported in the science journal Nature, shows the Y is an eroded version of the X chromosome with only a few genes. The X chromosome is also bigger than the Y and because females have two copies, one X chromosome is largely switched off or inactivated.

But not all of the genes on the silenced chromosome are inactivated, which could explain some of the differences between men and women, according to Laura Carrel, of Penn State College of Medicine in Pennsylvania who also reported her findings in the journal.