Proposed Number of Hox Genes in Some Extant and Extinct

Proposed number of Hox genes in some extant and extinct animal groups $\begin{array} { | c | c | c | c | } \hline \begin{array} { c } \text { Last Common } \\\text { Ancestor of Bilateria }\end{array} & \begin{array} { c } \text { Last Common Ancesto } \\\text { of Insects and } \\\text { Vertebrates }\end{array} & \text { Ancestral Verte brates } & \text { Mammals } \\\hline 4 & 7 & 14 & 38 \\\hline\end{array}$ Which of the following is the most parsimonious explanation for the change in the number of Hox genes from the last common ancestor of insects and vertebrates to ancestral vertebrates, as shown in the table provided?

A) the occurrence of two distinct duplications of the entire seven-gene cluster, followed by the loss of one cluster
B) two distinct duplications of a three-gene cluster of Hox genes, followed by an independent duplication of an individual Hox gene
C) the occurrence of seven independent duplications of individual Hox genes
D) the occurrence of a single duplication of the entire seven-gene cluster