Sex and Genes

October 24, 2011

Torah Kachur

The battle of the sexes goes beyond pop-psych books, beer commercials and war mongering.  The differences between males and females start at the level of our genes in ways we still don't understand.  The evolution of sexual reproduction (Thank Darwin for that) allowed more genetic mixing, more variation and ultimately more capacity for complex evolution but it created a problem - how do you make two individuals of the same species different enough to have different junk but same enough so they can breed?




The answer is the sex chromosomes - males of many species including mammals have one X chromosome and one piddly little Y chromosome that basically does nothing.  Whereas females have two X chromosomes making us clearly the better sex.  It also means that males only have one copy of the genes on the X chromosome as opposed to the normal two copies of every other gene.  This means that males are more prone to diseases of genes on the X chromosome like haemophilia or red-green colourblindness and also can fall victim to the rare Y chromosome encoded conditions like hairy ear rim.... lovely.


Clearly men have to try their best to keep up with women, usually they don't succeed and the XX organisms of the species are left trying to compensate for the failings of the 'other half'.  How can I possibly make such a bold claim?  It's science, people. A new paper published out of the Tar Heels stompin' grounds has continued to shed light on how males and females of mammals and other species compensate for a male's lack of an extra X chromosome.  Dr. Jason Lieb and team investigated the Ohno hypothesis that suggests that males of an XY species are left to try to upregulate, or double, their genetic contributions from their one X chromosome to compensate for their single copy.  While the females of the species also double the genetic expression, but then have to accommodate the males (again) by shutting down an entire X chromosome so that they have equal amounts to their lesser bedmates.


There are other species that use a different mechanism to compensate for the sex-specific gene dosage, like in all birds where the males have two copies of the same sex chromosome (called ZZ) while the females have one copy of each sex chromosome (called ZW) and perhaps male birds are better in this particular set of organisms - after all, they get the shiny feathers.  But I'll rest my case that women are the more accommodating and advanced sex for humans and all XX/XY species.


Deng, X., Hiatt, J., Nguyen, D., Ercan, S., Sturgill, D., Hillier, L., Schlesinger, F., Davis, C., Reinke, V., Gingeras, T., Shendure, J., Waterston, R., Oliver, B., Lieb, J., & Disteche, C. (2011). Evidence for compensatory upregulation of expressed X-linked genes in mammals, Caenorhabditis elegans and Drosophila melanogaster Nature Genetics DOI: 10.1038/ng.948



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