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Extra female gene creates insatiable male sex drive in mice

Eric Pfeiffer
The Sideshow

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(AP/Robert F. Bukaty)

Mice born with an extra female chromosome have much greater sex drives than their typical male counterparts, according to new research.

And even more interesting, the same findings may apply to human men with Klinefelter's Syndrome, who are genetically XXY, as opposed to the typical chromosome patterns of XY for males and XX for females. The findings were published in the latest issue of the journal Hormone and Behavior.

"Whether this is a specific phenomenon to mice, or even to this particular inbred background strain of laboratory mice, is still an open question, but we did find similar results in two different genetic models of mice," study researcher Paul Bonthuis, told LiveScience's Jennifer Welsh in an interview. "To know how general the finding is to other mammals, one would have to do studies with other mammalian species directly."

In the study, researchers found that males with the extra X female chromosome had nearly insatiable sex drives: They ejaculated nearly twice as much as their typical male counterparts, along with mounting females more frequently, and "showed more pelvic-thrusting motions" during sex.

It has typically been understood that male sex drive is determined by hormone secretion levels, rather than specific genetic makeup. And while those hormone secretions may still play a leading role in the sex drives of men and women, the new research indicates there may be additional factors affecting sexual activity that are still to be determined.

Bonthuis told LiveScience that the researchers are still trying to determine why the extra X chromosome is affecting male sexual behavior. "We do not yet know what gene on the X chromosome is causing this effect on behavior," Bonthuis said. "It is hard to say for certain what the X factor could be, but we do have some likely candidates."

Interesting, human men born with the double X chromosome often suffer from infertility and hypogonadism, aka lower testosterone levels. They are typically taller but with less developed and weaker muscles than the average male.

But a 1997 study on Klinefelter's found these men also reported having more sex than their typical XY male counterparts. Not all men with Klinefelter's display any or all of the above-described traits, however.

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