The best answer is A - body plan.
Hox genes also called homeotic genes are any group of genes which control the pattern of body formation in the early stages of embryonic development of organisms.
These genes code for a what are known as transcription factors that direct cells to form various parts of the body.
A homeotic protein has the ability to activate one gene but repress the other, producing effects which complement the development of organism.
Human have 39 hox genes divided into four separate clusters A, b, C, D, located on different chromosomes.
