How Do You Know Whether You Are Male or Female?

New research published online this week in the open-access journal PLoS Biology investigates this basic and much-studied question in the fruit fly, and comes to a surprising new conclusion.

In mammals, male or female development depends on the presence of the Y chromosome, which is only found in males because it includes masculinizing genes. But other animal groups have evolved different systems. James Erickson and Jerome Quintero at Texas A&M University studied the mechanism of sex determination in the fruit fly, Drosophila melanogaster.

Previous studies in the fly suggested that it was the ratio of X chromosomes (the “female” chromosome, of which there are two copies in a female fly, and just one in a male) to the non-sex chromosomes (the autosomes) that determined the sex of a fly embryo. However, this new paper indicates that rather than being dependent on the ratio, it is the number of X chromosomes that is important. Sex is determined during a very specific and short stage in embryo development, and only two X chromosomes can produce enough of a signal to feminize the embryo during this window of opportunity.

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Even Today, Couples Put More Emphasis on Husband's Career

Sociological research has shown that when couples move, the husband's career gets a boost, while the wife's career suffers. A University of Iowa professor investigated the reason behind the phenomenon and discovered that couples tend to put more emphasis on the man's career, even if the wife works full-time and is college-educated.

"This is bad news for people who are interested in men and women having equal success in the labor force," says Mary Noonan, associate professor of sociology in the UI College of Liberal Arts and Sciences. "Even for highly educated married women with prestigious occupations, employment still suffers when they move, while the husbands' careers benefit. These women likely share the role of breadwinner, earning a significant part of the family income, but their career is still seen as secondary within the dynamic of the couple."

Kimberlee Shauman, associate professor of sociology at the University of California at Davis, and Noonan reported the findings on their study on family migration in a recent issue of the journal Social Forces. Using data from the Panel Study of Income Dynamics, an annual survey that tracks families over a 30-year period, they examined the experiences of 5,072 working men and 4,120 working women between ages 25 and 59, all of whom were married. They compared the employment status and salaries of those who moved from one metropolitan area to another (655 men, 371 women) to those who stayed put.

They found that a year after the move, nearly all of the men remained employed, but the women who moved were 22 percentage points less likely to remain employed compared to women who didn't move. The men who moved boosted their salary by an average of $3,000 that year, compared to an average increase of only $700 for men who stayed put. But women who moved reported average salary increases of $750 less than women who stayed put.

"Our results support the notion that families migrate to enhance husbands' careers," Noonan says. "Women are very unlikely to initiate the move. They're more likely to be the 'trailing spouse,' following their husbands in a move for his promotion, raise, or better opportunities down the road."

Sociologists have speculated that the type of jobs men and women choose could be the reason moving can help husband's careers but hurt wives' careers, Noonan said. Perhaps men are more likely to choose more specialized or in-demand positions, jobs for which they might be recruited and that have a steeper salary ladder. On the flip side, it's possible that women more often choose fields like teaching, secretarial work, or nursing, positions for which more workers are qualified and that typically involve a more gradual salary increase.

To test that theory, Shauman and Noonan developed a way to control for the characteristics of the occupation. They found that even when the playing field was leveled in regard to the type of job, moving still hurt women's careers.

"Whether you're a female nurse or secretary or a female CEO, you're facing the same negative consequences after the move," Noonan says. "Even today, when women are earning more money and are more likely to put an emphasis on their career, when it comes to marriage, gender roles are very entrenched. People still buy into the stereotypes of what it means to be a good wife. It means that caring for your children and supporting your husband's career is viewed as a wife's main priority. Working is fine, but that's not really a wife's primary role."

In future research, Noonan would like to design a qualitative study to find out how couples weigh decisions on whose career matters more.

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