Hox genes are sometimes called "master switches". They have acquired this nickname because a single Hox gene will turn on (or off) several related genes. That means that a single Hox gene cannot have a large effect on phenotype.

A. True

B. False

Answer: B. False

Explanation:

"Hox" genes are a highly conserved group of genes, all of whose products are transcription factors bearing a specific domain (called a "homeodomain"). The transcriptional activity of a large amount of genes relevant to embryonic development is controlled by regulatory sites which are able to bind to this domain. Changes in the transcriptional activity of even a single Hox gene may thus have dramatic downstream effects on the phenotype, as this will result in several further genes having their transcription either enhanced or suppressed.