Genetics of Genitalia: he have one but lizards have two

Researchers at Harvard Medical School have been able to crucially understand why reptiles have genitalia structural different but functionally similar to that of mammals and birds. Snake and lizard genitalia are derived from tissue that gives rise to the legs while mammalian genitalia are derived form tissue that give rise to the tail bud. It turns out that the embryonic cloaca, which later becomes the urinary and digestive tract, issue molecular signals that tells neighboring cells to form the external genitalia. Since location determines which tissue receives the signal first it is different in mammal and reptiles. To confirm this the researchers grafted cloaca tissue next to the limb bud in one group of chicken embryos and next to the tail bud in another group. They found that in both cases cells closer to the grafted tissue partially converted towards a genitalia fate. Their findings confirmed their hypothesis that different populations of cells with progenitor potential are able to respond to cloaca signals and contribute to genitalia growth.

vestigial limb bud and hemipenis of an embryonic snake

The research was interesting and conclusive in showing that even though the genitalia is derived differently in mammals and reptiles, they are homologous in that they are derived from the same genetic programming.

Main article: http://www.sciencedaily.com/releases/2014/11/141105131941.htm

Related article: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13819.html