In Figure 1A, Kvon et al, showed a mouse embryo with human ZRS enhancer activity to express where in the embryo ZRS expression is located. To highlight the differences in the ZRS region and when they may have occurred evolutionarily, Figure 1B and 1C show a comparison in the ZRS region amongst the species and the phylogeny of these species, respectively, to better comprehend the progression of the loss of the limb enhancer. Through this it was found that the basal snakes ZRS enhancer was similar to limbed lizards and the substitution rate correlated with the other vertebrates, but the ZRS in the advanced snakes showed an increased number of substitutions compared to the other vertebrates. Overall every species of snakes has a ZRS enhancer and it was further exemplified that the separation between the basal and advanced snakes was based on the evolutionary constraint on the …show more content…
To determine how important this 17-bp deleted sequence is the researchers combined this sequence into the python enhancer sequence to see if the mouse model will then express limb development. This knockin experiment showed that the python enhancer with the 17-bp sequence showed normal limb development exemplifying that this sequence is a contributor to enhancer