The sex of human and other mammals is determined by a male-determining genes. The human Y chromosomes are degenerating and may disappear in a few million years if we don't change them.
Two branches of rodents have lost their Y chromosomes and are still alive.
The spiny rat has evolved a new male-determining genes.
The names of the males and females have nothing to do with their shape.
About 900 genes in the X are not related to sex. There are few genes and a lot of non-coding DNA in the Y.
The Y chromosomes have an important gene that kicks-starts male development.
After 12 weeks after conception, the master genes switch on others that regulate the development of a testis. The embryo makes male hormones that ensure the baby develops as a boy.
The sex region on the Y was identified as SRY. It works by triggering a genetic pathway starting with a gene called SOX9 which is key for male determination in all animals.
Our X and Y chromosomes are similar to those of most mammals, with an X with a lot of genes and a Y with SRY. The system has problems because of the way the X genes are distributed.
How did the system change? The platypus in Australia has different sex chromosomes than birds.
The XY pair is an ordinary chromosomes with two equal members. The mammal X and Y are thought to be ordinary pairs of chromosomes.
Over the 166 million years that humans and platypus have been evolving separately, the Y chromosomes have lost 900–55 genes. Five genes are lost per million years. The last 55 genes will disappear in 11 million years.
Our claim of the impending demise of the human Y created a furore, and to this day there are claims and counterclaims about the expected lifetime of our Y chromosomes.
There are two rodents that are still alive even though they have lost their Y chromosomes.
Both the mole voles of eastern Europe and the spiny rats of Japan have some species that have completely vanished. There is a single or double dose of the X chromosomes in both genders.
Although it's not clear how the mole voles determine sex without the SRY gene, a team led by Hokkaido University has had more luck with the spiny rat.
Most of the genes on the Y of spiny rats had been moved to other parts of the body. She didn't find any trace of SRY or the gene that replaced it.
They have published a successful identification. The team refined the sequence in the genomes of males and females and tested it on every rat.
There was a small difference between the sex genes on the spiny rat's chromosomes. There was a small duplication in all males and no females.
The switch that normally turns on SOX9 in response to SRY is contained in this small bit of duplicated DNA, according to them. They discovered that the change would allow SOX9 to work without SRY.
Speculation about our future has arisen due to the imminent disappearance of the human Y chromosomes.
Some lizards and snakes can make eggs using their own genes. Humans and other mammals have at least 30 genes that work only if they come from the father.
The end of the Y chromosomes means that we need sperm and men to reproduce.
There is a chance that humans can evolve a new sex determining genes. Oh yeah, phew!
Sex determining genes come with risks. If there are more than one new system in different parts of the world, what would happen?
The separation of new species is what has happened with mole voles and spiny rats.
If someone went to Earth in 11 million years, they wouldn't find any humans or any other human species.
Jenny Graves is a professor of genetics at La Trobe University.
Under a Creative Commons license, this article is re-posted. The original article is worth a read.
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