Question

the diagram shows hox genes and body segments in fruit flies. why does the developing embryo grow wings only in the thorax segment? a. only the cells in the thorax segment contain the genes needed to build wings. b. hox genes produce transcription factors that regulate genes for wings, so they are turned on only in the thorax segment. c. after the wings develop in the thorax segment, hox genes turn off those genes in the other segments. d. the genes for building wings are used first in the thorax segment, and then transcription factors block them from being used again.

Explanation:

Hox genes act as master regulators. They produce transcription factors. These factors control the expression of wing - related genes. In fruit flies, this regulation occurs specifically in the thorax segment. Option A is incorrect as all cells (except red blood cells) have the same genome. Option C is wrong because Hox genes regulate the development, not turn off genes in other segments after wing development. Option D is also incorrect as it misrepresents the role of Hox genes in regulating wing - gene expression. Hox genes are involved in the initial regulation of wing - gene expression in the thorax, not in blocking gene use after initial use.

Answer:

B. Hox genes produce transcription factors that regulate genes for wings, so they are turned on only in the thorax segment.