University scientists in Japan recently published a paper claiming the Y chromosome — a sex chromosome which is normally present only in male cells, which are designated XY — has disappeared from a species of a rat.
And now, genetic scientists are curious to learn if this phenomenon in rats could lead to the eventual end of human males.
Human beings possess 23 pairs of chromosomes, with one pair representing the sex chromosomes.
Mammals don't start as females. Instead, their development begins with a blank slate of XX or XY genetic code; and within the first six weeks of gestation, "only the X gene" becomes apparent.
However, when the Y gene for males starts expressing, "it releases androgens like testosterone, represses some X gene expression (and estrogen development), and expresses specific Y genes," according to FactMyth.com.
This process leads to sexual differentiation.
"The mammal Y is a weird little chromosome with hardly any genes on it and a lot of DNA junk. But one of these genes is SRY, the male-determining gene," Jenny Graves, a sex chromosome geneticist at La Trobe University in Melbourne, Australia, told Newsweek.
"The Y makes no sense in terms of function, but is easy to understand in terms of evolution. The X and Y were once upon a time just an ordinary pair of chromosomes. Then one partner acquired a variant gene (SRY) that determines maleness," said Graves.
The geneticist then added: "Other genes handy in males accumulated nearby and to keep this male-specific gene package intact, it stopped swapping bits with the X. This meant it was stuck in a rut and couldn't repair itself, so it degenerated very rapidly, with many mutations and deletions, leading to its present pitiable state."
In humans, the SRY gene — which "provides instructions for making a protein called the sex-determining region Y protein" — remains on the "Y" chromosome.
"When humans run out of Y chromosome, they might become extinct — if we haven't already extincted ourselves long since — or they might evolve a new sex gene that defines new sex chromosomes," said Graves.
Despite the Japan team's findings among rats, the genetic code for humans isn't expected to dissipate anytime soon, according to Root Gorelick, a sex evolution researcher at Carleton University in Canada.
"Females, by which I here mean organisms that produce large gametes called egg cells, can — in some species — self-fertilize, either by the egg nucleus fusing with another egg nucleus or by the egg nucleus spontaneously doubling all of its chromosomes," Gorelick told Newsweek.