Scientists discover oldest animal sex chromosome dating back 380 million years

Scientists have discovered the oldest animal sex chromosome, and its age is truly staggering.

Researchers have uncovered the octopus Z chromosome dating back around 380 million years and comes from the animal’s ancient ancestor.

The research into cephalopods could answer how the sex of animals in this fascinating group is determined – and it turns out that genes are involved, of which there was no evidence before.

In humans, the sex chromosomes determine whether someone is born male or female. But while X and Y chromosomes play a key part in humans, it wasn’t known before how the sex of cephalopods was determined.

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While scientists believed that temperature of water could have played a role like it does for some species of fish, the new findings represent a major new development.

Evolutionary geneticist Andrew Kern at the University of Oregon in Eugene said [via Nature]: “We stumbled upon probably the oldest animal sex chromosome known to date.

“Sex determination in cephalopods, such as squids and octopi, was a mystery — we found the first evidence that genes are in any way involved.”

The researchers found that W chromosomes do not exist in female octopuses, which in turn suggested that ZZ sex chromosomes are present in males.

“This pattern suggests that the Z chromosome evolved once in the lineage that led to modern squid and octopuses — after this lineage split off from hard-shelled nautiloids,” says Kern.

The findings also show that the Z chromosome was present between 450 million and 250 million years ago, which is far older than the previous oldest known animal sex chromosome which existed in sturgeon fish around 180 million years ago.

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