Duplication of Hox genes made increased morphological complexity possible.
Explanation:
The hox gene cluster consists of a group of related genes that function to controls the basic body plan of an embryo and also define the head to the tail axis.
These are mainly responsible for ensuring the correct position of al the structures in the body.
Since the anterior-posterior axis all the vertebrates are established by these hox genes this points out to the fact that common information is needed amongst all he vertebrates to define the various morphological variations that occurred.
The hox genes have shown duplication in the course of evolution and they have undergone a four-fold duplication which has led to the generation fo different structures in the various organism and is thus responsible for the increased morphological complexity.
