A rat without a Y chromosome could be a glimpse of our genetic future

The person is Michael Le Page.

The loss of the Y chromosomes means the loss of males and the demise of the species. The Amami spiny rat doesn't have a Y chromosomes. Hokkaido University in Japan has shown that one of the rat's normal chromosomes has been turned into a male sex chromosomes.

The Y chromosomes in many mammals, including us, have been decreasing over the last tens of millions of years. The spiny rat is showing how this could happen.

Sex is determined by the X and Y chromosomes in almost all mammals. An embryo that has two X chromosomes will become a female. It becomes male if it has an X and a Y.

The SOX9 gene that causes the development of testes is found on the Y chromosomes.

The Amami spiny rat is one of only a few mammals that don't have Y chromosomes. There is only one X chromosomes for females and males.

Female mammals show that the shrunken Y doesn't have any important genes, so cells and individuals can survive its loss. Recent studies show that it is lost from cells as men get older. The Y should be lost because there would be no more males.

In order to find out how male rats still exist, Kuroiwa and her team first looked at the genomes of several males and females. One of the two copies of chromosome 3 has a duplicated region in male rats.

Adding the duplicated region to mice was one of the experiments done by the team. The version without the duplication is referred to as a "proto-X" while the version with the duplication is referred to as a "proto-Y".

To show that no males develop, the team would have to remove the duplicated rats from the petri dish. The spiny rat is an important species and can't be studied in such a way. The evidence they have is convincing.

Previous attempts to find out how male spiny rats became male have come up blank because of copy number variations.

After 2 million years ago, the spiny rats split from the related species that still have a Y chromosome. The loss of the Y would not result in the loss of all males once it was duplicated. A group of males with and without a Y may have been present on the island.

Males with no Y died off as a result of rising seas. The land area was much smaller in the past due to the rising sea level.

This is a great work of art. Jenny Graves, a lecturer at La Trobe University in Melbourne, Australia, made a controversial claim in 2002 that the human Y chromosomes will be lost in 10 million years. She says there is no reason to think our Y chromosome is any stronger than the spiny rat's.

Kuroiwa agrees with Jenny. I think that the Y chromosomes will disappear.

According to a number of studies, the Y chromosomes is in no danger of being lost by us or other mammals. The paper makes it clear that the loss of a Y chromosomes is very rare in mammals.

The Amami spiny rat has only one X chromosomes and this could be lost over time. According to Kuroiwa, he thinks that X will eventually disappear due to its unstable nature.

The descendants of the Amami spiny rat are likely to evolve along the same lines as the X and Y.

The journal is titled PNAS and it can be found at 10.1073/pnas.