Washington, July 17 - The sex chromosome that only males carry is deteriorating and could disappear within a few million years.

A pair of Penn State University (PSU) scientists discovered that the male Y chromosome evolved at a much more rapid pace than X chromosome, which both males and females carry.

This rapid evolution of the Y chromosome has led to a dramatic loss of its genes at a rate that could eventually lead to its disappearance.

The team includes Kateryna Makova, associate professor who led the research and National Science Foundation graduate research fellow Melissa Wilson.

'There are three classes of mammals,' said Makova. 'Egg-laying mammals, like the platypus and the echidna; marsupials, like the opossum and the wallaby; and all other mammals -- called eutherians -- which include humans, dogs, mice, and giraffes.

The X and Y chromosomes of marsupials and eutherians evolved from a pair of non-sex chromosomes to become sex chromosomes.'

Humans have 23 pairs of chromosomes, which are the structures that hold our DNA, but just one pair of these chromosomes are sex chromosomes.

'In eutherian mammals, the sex chromosomes contain an additional region of DNA whereas, in the egg-laying mammals and marsupials, this additional region of DNA is located on the non-sex chromosomes,' said Makova.