American scientists from the University of Oregon have discovered the oldest known animal sex chromosome; The octopus Z chromosome, which first appeared in the ancient ancestor of modern cephalopods about 380 million years ago. The study was published in the scientific journal magazine Nature.
“We have found the oldest animal sex chromosome known today. Determining sex in cephalopods such as squid and octopus has been a mystery; we have found the first evidence that genes are somehow involved,” says evolutionary geneticist Andrew Kern, a co-author of the paper.
In many animals, including most mammals and some insects, sex chromosomes determine whether an individual will be male or female.
In humans, women usually have two sex X chromosomes, while men usually have one X and one Y sex chromosome.
But until recently, they did not know how some animal groups determine the sex of their individuals. These include cephalopods – octopuses, squids and nautiluses.
The team found Z chromosomes in some other octopus and squid species, but not in the nautilus.
“This model suggests that the Z chromosome once arose in the lineage that gave rise to modern squid and octopuses, then the lineage diverged from the hard-shelled nautiloids,” Kern said.
This means that the Z chromosome first appeared between 450 and 250 million years ago and persists until the present day.
The oldest animal sex chromosome ever known was thought to have originated in sturgeon about 180 million years ago.
Previous scientists opened A new species of vampire squid that is 183 million years old.