Chapter 18, Problem 16P

The pair $-$ rule gene fushitarazu is expressed in the seven even $-$ numbered parasegments during Drosophila embryogenesis. In contrast, the segment polarity gene engrailed is expressed in the anterior part of each of the $14$ parasegments. Since both genes are active at similar times and places during development, it is possible that the expression of one gene is required for the expression of the other. This can be tested by examining expression of the genes in a mutant background $-$ for example, looking at fushitarazu expression in an engrailed mutant background, and vice versa.

a. Given the hierarchy of gene action during Drosophila embryogenesis, what might you predict to be the result of these experiments?

b. Based on your prediction, can you predict the phenotype of the fushitarazu and engrailed double mutant?