Molecular Biology of the Gene 7th Edition by Richard Losick, James Watson, Michael Levine, Tamara Baker, Alexander Gann

Exercise 11

Bicoid mRNA is maternally derived and localized to the anterior of early Drosophila embryos. Bicoid protein is a concentration-dependent transcriptional activator of the hunchback gene.
Depicted below are embryos in which a reporter is expressed under the control of the wild-type hunchback promoter. The darkened regions indicate reporter expression. Use these patterns to answer the following questions.

A. Which expression pattern would you expect in embryos from a mother that does not express bicoid mRNA? Explain.
B. Drosophila flies are diploid organisms. This results in a pattern of reporter expression that most closely resembles pattern C. Would you expect this pattern to change if the mother had only one copy of the bicoid gene? If no, explain why not. If yes, explain and select the most likely expression pattern from the choices above.
C. The hunchback promoter contains high-affinity and low-affinity binding sites for Bicoid protein. Which expression pattern would you expect if the hunchback promoter was mutated so that it now contains only the low-affinity binding sites for Bicoid protein and the mother has two copies of the bicoid gene? Explain your choice.