Large portions of the X chromosome - long perceived as the "female" counterpart to the male-associated Y chromosome - have evolved to play a specialised role in sperm production, a new study claims.
New analysis of the genetic sequence of the X chromosome reveals that despite its reputation as the most stable chromosome of the genome, the X has actually been undergoing relatively swift change.
"We view this as the double life of the X chromosome," said Whitehead Institute Director David Page, whose lab conducted this new study.
"The X is the most famous, most intensely studied chromosome in all of human genetics. And the story of the X has been the story of X-linked recessive diseases, such as colour blindness, hemophilia, and Duchenne's muscular dystrophy," Page said.
"But there's another side to the X, a side that is rapidly evolving and seems to be attuned to the reproductive needs of males," he said.
Researchers embarked on a rigorous comparison of the mouse and human X chromosomes, in part to test the longstanding biological tenet that the gene content of X chromosomes is conserved and shared across mammals, Phys.Org reported.
Page and colleagues devised what is known as SHIMS (single-haplotype iterative mapping and sequencing) to establish a definitive reference DNA sequence of the Y chromosome.
The lab greatly improved the human X reference sequence, accurately assembling three large amplicons, identifying previously unknown palindromes, and ultimately shortening the entire length of the sequence by eliminating four major gaps.
Expression analyses revealed that these genes are active almost exclusively in testicular germ cells, where, at a minimum, they likely contribute to sperm production.
Researchers said these results suggest that it's time to re-examine the biological and medical importance of the X chromosome.
The study was published in the journal Nature Genetics.
