Tuesday, 22 May 2012

Make men more masculine with an extra female X chromosome

We all know that chromosomes can be divided into two types, autosomes and sex chromosomes. Human contain 22 pairs of autosomes and only one pair of sex chromosomes. The autosomes are not involved in sex determination while the sex chromosome contain X and Y which is a combination determine the sex of an individual (Reece et al, 2012, pp.253-254). Females have two of the same type of sex chromosome (XX), while males have two dissimilar sex chromosomes (XY) and it produces different hormones.

Figure 1: Human X&Y Chromosomes (Trafton, 2010)

The article ‘extra female genes make men more masculine’ has grabbed the headlines in recent days. The research found that there are few men who have an extra X chromosomes known as Klinefelter's Syndrome (Lippincott, 2009, p.1141). The syndrome can affect different stages of physical, language and social development. However, these extra second X chromosome makes male mice more masculine which is an unexpected effect. According to Rissman at the University of Virginia, hormones play a role in behaviour which makes distinct differences between female and male. It suggests that sex chromosomes may give an impact on behaviour that extends beyond the effect of hormones (Hamzelou, 2012).

             The chemical messenger produced by an endocrine cell is called hormones which regulate bodily function and has a specific effect on organs directly influence on behaviour. Most men produce testosterone from four weeks old and it helps the growth and development the uniqueness of male body such as greater muscle mass (Bardi, 2012). Female produces estrogens in ovaries are accountable for the development of female sexual characteristics (Bardi, 2012).

             As New Scientist reports, male mice has two X chromosomes instead XY show more masculine sexual behaviours when mutation in mice happened (Hamzelou, 2012). They ejaculate faster, more ejaculation and frequencies of mounts and thrusts than other single X chromosome male mice. This is caused by the region of sex-determining of the Y chromosomes of male which shifted to a non-sex chromosome but had same level of testosterone as your average XY mice. To confirm the experiment, they did the research compared XY with XXY male mice and also XXY mice showed more sexual behaviours.

Figure 2: World’s Hottest Male Athlete (Anon, 2009)
             Since, the researchers found the same effect in both XX and XXY mice which means Y chromosome is independent. Instead, whatever is making those mice act more aggressively masculine can be traced to their female sex chromosome. It's an open question whether this effect may holds in human and also can be answered why male with Klinefelter's Syndrome more likely to have sex than other male.


Anon, 2009, World’s Hottest Male Athlete‘, viewed 20 March, <http://waynejoseph.wordpress.com/2009/08/14/>.

Bardi J, 2012, Male and Female Behaviour Deconstructed, viewed 20 March 2012, <http://www.ucsf.edu/news/2012/02/11440/male-and-female-behavior-deconstructed>.

Hamzelou J, 2012, Extra genes make men more masculine, viewed 15 March 2012, < http://www.newscientist.com/article/mg21328553.600-extra-female-genes-make-men-more-masculine.html>.

Lippincott W & W, 2009, Professional guide to diseases, 9th edn, Wolters Kluwer Health, p. 1141.

Reece JB, Urry LA, Cain ML, Wasserman, SA, Minorsky PV, Jackson, RB & Campbell NA, 2010, Campbell Biology, 9th edn, Pearson Education, pp. 253-254.

Trafton A, 2010 Y chromosome evolving rapidly MIT News, viewed 20 March 2012, <http://web.mit.edu/newsoffice/2010/y-chromosome-0114.html>.

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