Y Chromosome

For more than 20 years, I've been writing about local history, and never once has Southern California let me down. I've found no shortage of tycoons and beggars, dreamy spiritualists, mad-eyed killers. This 227-year-old city has had a few angels, but it's the others who often make for the most fascinating storytelling.

Of all the obstacles athletes have had to overcome to compete in the Olympics, perhaps the most controversial has been the gender test. Originally designed to prevent men from competing in women's events, it is based on the premise that competitors can be sorted into two categories via established scientific rules. But the biological boundaries of gender aren't always clear. Consider the Spanish hurdler Maria Jose Martinez-Patiño. A gender test revealed that she had a Y chromosome, which normally makes a person male.

Every man on Earth today is related, linked by a Y chromosome to a common ancestor who lived about 190,000 years ago, a study suggests. This so-called ancestral Adam was among many males who lived before anatomically modern humans evolved, but he's the only one purported in the study to have a genetic legacy that persists today.

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.

Male mice have been created from female embryos by the injection of a single gene into fertilized eggs, confirming that the gene is the long-sought "sex trigger" that determines gender, British researchers reported last week in the journal Nature. Two "female" embryos developed male sex organs, and a third grew up to show normal male mating behavior, although all were infertile. The gene appears to work by regulating the activity of other genes involved in development.

When modern humans left Africa as far back as 70,000 years ago, they dispersed across the world, reaching Australia 50,000 to 40,000 years ago. From then until the 18th-century arrival of European colonists, aboriginal Australians did not mix their DNA with anyone else in the world - or so many scientists believed. Now a study has turned up evidence of much more recent interbreeding between native Australians and people who came from India. The findings, based on a detailed examination of the DNA of aboriginal Australians and hundreds of people of other pedigrees, found that mixing occurred as recently as 4,200 years ago. Reported in the journal Proceedings of the National Academy of Sciences, the results dovetail with interesting archaeological and fossil changes, said study leader Mark Stoneking, a molecular anthropologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

New blood sampling methods may offer a safer, easier way of determining an unborn baby's sex, but more work is needed before the tests will be available in doctors' offices, researchers said last week. Current prenatal tests used to check for sex and genetic defects, like Down's syndrome, require withdrawing fluid or tissues from a pregnant woman in areas near her developing fetus. Such procedures pose a risk of infection and other complications due to their invasive nature.

Girls are more socially adept than boys because they have the right genes, British researchers report in the June 12 Nature. Research on girls with Turner's syndrome showed a genetic link with social ability, they said. Healthy girls get one X chromosome from each parent, but girls with Turner's have only one good X chromosome. The team tested 80 girls with Turner's for social skills.

Q: Why do men have nipples? Is it true that the father of a motherless child can sometimes nurse the baby? A: Human embryos are female at conception and become male only when exposed to hormones produced by genes on the Y chromosome. But because the basic blueprint was female, males retain some remnant structures of the female, such as the breasts.

A new technique that separates male-producing sperm from female-producing sperm based on small differences in the weight of their DNA can greatly increase the likelihood of conceiving a daughter, Virginia scientists said Wednesday. Sperm containing a Y chromosome, which produces males, have about 2.8% less genetic material than sperm containing an X chromosome, which produces females. Researchers from the Genetics & IVF Institute in Fairfax, Va.