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Extra female genes make males more masculine

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  • Chris & Christine
    Extra female genes make men more masculine 09 March 2012 by Jessica Hamzelou Magazine issue 2855. Subscribe and save For similar stories, visit the Genetics
    Message 1 of 1 , Mar 9, 2012

      Extra female genes make men more masculine

      NOW here's a brain bender: an extra set of female genes appears to make males more masculine. The surprising discovery suggests that sex chromosomes play a role in directing behaviour that extends beyond the effects of hormones.

      "The predominant idea is that the difference between male and female behaviours is down to hormones," says Emilie Rissman at the University of Virginia in Charlottesville. This starts early in life - male fetuses are exposed to testosterone from 4 weeks old, while females are not.

      To find out if sex chromosomes play a role in sex-specific behaviours beyond dictating which hormones are present, Rissman's team took advantage of a mutation in mice that causes the sex-determining region of the male Y chromosome to jump to a non-sex chromosome. The mice are male but have two X chromosomes.

      While these XX male mice had the same level of testosterone as normal XY mice, they displayed more masculine sexual behaviours - mounting females more often and ejaculating more frequently.

      To confirm that the differences were a result of a hidden factor on the X chromosome and not the lack of a Y chromosome, the team compared XY male mice with XXY male mice, which carry an extra X chromosome. Sure enough, the XXY mice also showed more male sexual behaviours (Hormones and Behaviour, DOI: 10.1016/j.yhbeh.2012.02.003).

      The finding tallies with research that suggests a female's second "inactivated" X chromosome may actually express a quarter of its genes. These could alter the expression of genes on other chromosomes, and might be partly responsible for behavioural differences between the sexes, says Rissman.

      "The extent to which these findings are generalisable to humans remains to be seen," says William Davies at Cardiff University, UK. However, the idea may provide an explanation for evidence that XXY men have more sex than men with the regular XY.

      If Rissman's team can identify a region of the X chromosome that is linked to sexual activity, its protein products could be a target for libido-boosting therapies.

      Int J Androl. 1997 Apr;20(2):80-5.

      Sexual function and clinical features of patients with Klinefelter's syndrome with the chief complaint of male infertility.


      First Department of Urology, Toho University School of Medicine, Tokyo, Japan.


      In this report, we present the overall sexual function and clinical features of patients with Klinefelter's syndrome with the chief complaint of male infertility. The study consisted of 40 patients with a control group of 55 infertile non-azoospermic males with a normal 46,XY karyotype who visited the Reproduction Center of Toho University Hospital during the 5.5-year period between January 1991 and June 1996 with the chief complaint of male infertility. Among the 40 patients with Klinefelter's syndrome, 38 cases were pure 47,XXY, one case was 47,XXY with a pericentric inversion of chromosome 9 and one case was a mosaic of 46,XY/47,XXY(2:28). Thirty-nine of these 40 patients were azoospermic and one (47,XXY) had severe oligoasthenozoospermia. The sexual function of the patients was evaluated according to their responses to a preliminary questionnaire devised by our department. There was no significant difference in the frequency of sexual function disturbances between the patients with Klinefelter's syndrome and the control group (67.5% vs. 60.0%; chi 2 analysis; p = 0.454). The mean frequency of sexual intercourse per month in the patients with Klinefelter's syndrome was significantly higher than in the control group (4.4 +/- 2.8 vs 3.3 +/- 1.6: Welch's t-test, p < 0.05). A possible explanation for this variation may lie in the fact that many of these patients were diagnosed with azoospermia poor to the administration of the questionnaire and may have wished to continue to have relations as a couple.

      [PubMed - indexed for MEDLINE]

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