Answer:
a. hox genes.
Explanation:
HOX genes have the following functions:
The vertebrates are highly preserved.
The clusters and other genes occur uninterrupted.
Evolutionary, the heterogeneous regulatory areas between the genes most previously present are larger and more preserved than those present at the other ends of the clusters.
The characteristical feature is that these are homeodomain proteins with a highly preserved area of DNA binding encoded with homeobox gens.