Men are slowly losing their Y chromosome, but a new sex gene discovery in spiny rats brings hope for humanity

Subject : Science and Technology

Context:

The sex of human and other mammal babies is decided by a male-determining gene on the Y chromosome. But the human Y chromosome is degenerating and may disappear in a few million years, leading to our extinction unless we evolve a new sex gene.

What are chromosomes?

Chromosomes are the genetic material present in all cells. They are present in the nucleus of a eukaryotic cell. They are a thread-like structure.
Each chromosome of a eukaryotic cell contains DNA and associated proteins, known as histone proteins. They are responsible for the hereditary traits and passed from parents to offspring from one generation to another.
Humans have 22 pairs of numbered chromosomes (autosomes) and one pair of sex chromosomes (XX or XY), for a total of 46.
- Each pair contains two chromosomes, one coming from each parent, which means that children inherit half of their chromosomes from their mother and a half from their father.

How the Y chromosome determines human sex:

In humans, as in other mammals, females have two X chromosomes and males have a single X and a puny little chromosome called Y.
The X stood for “unknown”.
The X contains about 900 genes that do all sorts of jobs unrelated to sex.
But the Y contains few genes (about 55) and a lot of non-coding DNA — simple repetitive DNA that contains an all-important gene that kick-starts male development in the embryo. At about 12 weeks after conception, this master gene switches on others that regulate the development of a testis.
The embryonic testis makes male hormones (testosterone and its derivatives), which ensures the baby develops as a boy.
This master sex gene was identified as SRY (sex region on the Y) in 1990.
It works by triggering a genetic pathway starting with a gene called SOX9 which is key for male determination in all vertebrates, although it does not lie on sex chromosomes.

The disappearing Y:

In another mammal i.e. platypus, the number of X and Y chromosomes are equal.
This must mean the Y chromosome has lost 900–55 active genes over the 166 million years that humans and platypus have been evolving separately.
That’s a loss of about five genes per million years. At this rate, the last 55 genes will be gone in 11 million years.

Rodents with no Y chromosome:

Two rodent lineages that have already lost their Y chromosome – and are still surviving.
Although it’s not yet clear how the mole voles determine sex without the SRY gene.

What does this means for the future of men?

Some lizards and snakes are female-only species and can make eggs out of their own genes via what’s known as parthenogenesis.
But this can’t happen in humans or other mammals because we have at least 30 crucial “imprinted” genes that work only if they come from the father via sperm.

Chromosomal disorders: (Numerical abnormalities)

Chromosomal disorder: (Structural abnormalities)