Open Scott Roy’s Twitter bio and you’ll see a simple yet revealing phrase: “The more I learn, the more confused I get.” Now the rest of the scientific world may share in his confusion.
San Francisco State University’s associate professor of biology, published earlier this month in one of the scientific world’s most prestigious journals, catalogs a strange and confusing system of genes in a tiny rodent that scientists have ignored for decades.
“This is actually the strangest sex chromosome system known to science,” said Roy. “Nobody ordered this.” But he serves it anyway. The owner of those chromosomes is the creeping field mouse, a burrowing rodent native to the Pacific Northwest.
Scientists have known since the 1960s that the species had a number of strange genes: their number of X and Y chromosomes (bundles of DNA that play a major role in determining sex) differs from what is expected in male and female mammals .
The finding caught Roy’s attention when presented by a guest speaker at a San Francisco state seminar, and he realized that modern technology could shed new light on the mysteries lurking in the voles’ DNA.
After working with collaborators to unravel the voles’ genetic history – resulting in one of the most fully sequenced mammalian genomes in existence, according to Roy – the story only got weirder.
The team found that the X and Y chromosomes had fused in rodents sometime in the past, and that in males the X chromosome began to look and act like a Y chromosome.
The number of X chromosomes in male and female voles also changed, along with smaller pieces of DNA exchanged between them. The researchers published their results in Science on May 7, 2021.
Such profound genetic changes are exceptionally rare: the way genes determine sex in mammals has largely remained the same for about 180 million years, Roy explains.
“Mammals, with a few exceptions, are pretty boring,” he said. “We used to think that such a thing is impossible.” So how did this humble rodent’s genes get so jumbled together? It is not an easy question to answer, especially since evolution will no doubt produce some strangeness by chance.
However, Roy is determined to find out the ‘why’. He suspects that what the team found in the field mouse’s genome is something like the aftermath of an evolutionary battle for dominance between the X and Y chromosomes.
The study couldn’t have happened, Roy says, without collaborating with Oregon fish and wildlife biologists who had a creeping vole sample in a lab freezer.
He was also working with a group from Oklahoma State University when the two groups started talking about stealthy full DNA sequences posted on the Internet – and both realized they were working on the same question.
Another key was working at an education-oriented institution. Roy says he has time to develop ideas with colleagues and students at SF State, and that he can do research that he doesn’t know exactly what to find.
“This is a great example of non-hypothesis-based biology,” explained Roy. “The hypothesis was,” This system is interesting. I bet if you looked at it a little more there would be other interesting things. “It won’t be the last time Roy’s lab is in trouble.
” He and his associates plan to look into the genomes of other voles related species to map the evolutionary path that led to this strange system. He will also continue to DNA sequence curiosities in the tree of life.
“These bizarre systems give us a starting point to begin to understand why the more general systems are the way they are and why our biology works the way it works,” he explained.