Enhancer evolution

The gene pitx1 is a switch for skeleton patterning (it is a transcription factor that controls a battery that patterns mesodermal tissues)9. Loss of a cis regulatory element that turns it on in pelvic regions leads to a reduced pelvis. This mutation is common in freshwater fish populations, where a smaller pelvis may be beneficial, but not in marine fish populations, where a more robust pelvis may be beneficial.https://scholarlycommons.pacific.edu/open-images/1021/thumbnail.jp