October 2015 article on Doug Menke’s lab “Snake Genomes Reveal Shared Plans for Making Legs, Penises”
Penises and limbs are clearly very different (exaggerated references to third legs aside), but they develop in similar ways. They both involve long bits of tissue that grow out from a small embryonic bud, under the direction of very similar proteins, and molecules. Carlos Infante and Douglas Menke from the University of Georgia has shown that similar enhancers—sequences that switch genes on or off—are also at work in both organs.