Table 321 Proposed Number of Hox Genes in Various Extant and and Extinct

Table 32.1. Proposed Number of Hox Genes in Various Extant and Extinct Animals

-Two competing hypotheses to account for the increase in the number of Hox genes from the last common ancestor all bilaterians to the last common ancestor of insects and vertebrates are: (1) a single duplication of the entire 4-gene cluster, followed by the loss of one gene, and (2) 3 independent duplications of individual Hox genes. To prefer the first hypothesis on the basis of parsimony requires the assumption that

A) the duplication of a cluster of four Hox genes is equally likely as the duplication of a single Hox gene.
B) there is an actual process by which individual genes can be duplicated.
C) genes can exist is spatial groupings called "clusters."
D) clusters of genes can undergo disruption, with individual genes moving to different chromosomes during evolution.