This week in class we explored a paper written by Chris J. Cretekos et al. The article was called "Regulatory divergence modifies limb length between mammals," and looked at the limb-specific transcriptional enhancer Prx1 found in mice and compared it to the orthologous gene found in bats. What they found was that when the bat sequence of Prx1 was inserted into the mice, transcript levels in developing forelimbs was much higher and that the forelimbs themselves were also longer compared to the controls. It was also found that when the Prx1 gene was deleted in mice normal forelimbs developed. Overall, this article supports the claim that cis-regulatory are important in generating morphological differences between species.