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. Last Updated: 07/27/2016

Study Casts Light on Y Chromosome

In scientific circles, the Y chromosome -- the essence of masculinity -- is scorned as the runt of the human genetic family, so henpecked by mutations that it is wasting away.

So little respect does this small, self-absorbed chromosome command that scientists investigating the human genome felt free to jeer or mostly ignore it -- until now.

In research made public Wednesday, scientists confessed that they have sorely misjudged this single-minded sex specialist. After six years of laboratory work, scientists at the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, and the Washington University School of Medicine in St. Louis presented the complete genetic sequence of the Y chromosome, the first human chromosome to be thoroughly decoded.

They revealed that the tiny chromosome responsible for the male of the species is more subtle, robust and complex than previously believed. It has a unique way of keeping its indispensable genes intact, they found, that sidesteps the conventional genetic shuffling on which all other chromosomes depend.

Their discoveries are prompting researchers to rethink the genetic basis for the myriad differences between men and women in anatomy, physiology, cognition, behavior and disease susceptibility. There is an order to what had seemed to so many researchers before to be relentless decay. The DNA that many had dismissed as junk has genetic meaning.

The Y chromosome harbors up to three times as many genes as commonly thought, the researchers said. Moreover, it is evolving in an unconventional way at a speed that no one had imagined.

The findings, detailed in two research papers published Thursday in the journal Nature, upset some basic assumptions about the molecular biology of sex.

"It knocked me out of my chair the first time I heard it," said Brandeis University biologist James Haber, who studies how genes reproduce and repair.

The relationship between the Y chromosome, which triggers male development in an embryo, and the X chromosome, which is responsible for female development, is a mystery that has been unfolding for over 240 million years. Over the ages, they have gone quite separate ways.

The X chromosome today dwarfs its dwindling male counterpart. Indeed, nearly half of all genes related to the earliest stages of sperm production reside not on the male sex chromosome as might be expected, but on the female.

In all, there are 46 human chromosomes. In women, they are mated in 23 matching pairs. Through sexual recombination, when sperm and egg are created, the regular chromosomes and the X chromosome draw on their matching counterparts for genetic repairs.

But in perhaps the most intriguing new finding, Whitehead biologist David Page, who led the consortium of research teams, and his colleagues discovered that the male chromosome evolved its own way of repairing itself.

So far, researchers have analyzed only one man's Y chromosome. As others come under detailed scrutiny, Page and his colleagues expect to uncover considerable variation from one man to the next.