[
Science,
1995]
The contrasts between the sexes have inspired countless plays, novels, and other creative works. Sex differences inspire a group of developmental biologists, too-but there's a twist. While artists and most of the rest of us are fascinated by the effects of the male-female divide, these biologists are trying to learn how it arises in the first place. Their goal: to trace out the gene pathways that turn an embryo into a male or female. This quest has recently become one of the hottest areas of developmental biology, as two meetings held this year and devoted solely to the subject attest.
[
Science,
1995]
Sex has lots of advantages, as the number of species that indulge in it shows. But it also poses a potentially lethal problem. Most species use distinct X and Y sex chromosomes to determine who develops as female and who as male-and the female generally has more copies of the X chromosome than the male. But the X chromosome contains many genes needed equally by males and females, threatening females with what could be a lethal excess of X-chromosome gene products-or males with an equally serious deficiency. Researchers have known for decades that humans and other sexually reproducing species survive because of a correcting mechanism known as "dosage compensation" that equalizes the expression of X-linked genes between the sexes. But only now are they beginning to figure out how