Limbed animals use the same genetic elements to regulate the development of their limbs and genitalia.

Credit: Carlos R. Infante

Douglas Menke and his colleagues at the University of Georgia in Athens studied the genomes and embryos of mice, Anolis lizards and snakes (pictured). They found that in mice and lizards, many genetic regulatory elements are similarly active in the development of the limbs and the phallus. They also saw this pattern of activity in the external genitalia of the snake embryo (pictured, arrow).

Even though snakes lost their limbs during evolution, they probably retained the relevant genetic elements because of their importance for phallus development.

Dev. Cell http://doi.org/743 (2015)