An example of heterochrony is the difference in duration of brain growth between chimpanzees and humans. There is no doubt that heterochrony plays a significant role in the generation of evolutionary differences. Genetic variation has been found in two key regulatory genes that function in the somatropic growth axis. How the genetic variants produce differences in body size are not known. Alternatively, some genes may function only to create quantitative variation by tweaking the efficacy of key genes.
Many genes are redundant, since knocking out some genes result in no obvious phenotype.
This genetic redundancy could serve to maintain quantitative variation in the species. A species with an abundance of quantitative variation would be better equipped to adapt through natural selection in the presence of environmental pressure. Five QTLs that associate with variation in bristle number have been mapped to Chr 3. Genes that map nearby and are known to be involved in bristle formation were selected as candidate genes. One of the candidate genes is Delta .