Bicoid mRNA is maternally derived and localized to the anterior of early Drosoph
ID: 180570 • Letter: B
Question
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.Explanation / Answer
Answer 1. Pattern A.
Bicoid protein is transcriptional activator of hunchback protein. Hence, in the absence of bicoid protein, no expression of hunchback protein takes place.
Answer 2. Yes, change in the pattern is expected. Expected pattern is B
Changing the copy number of bicoid gene to one from two will make change in the pattern because bicoid protein acts as a concentration dependent transcriptional activator of hunchback protein. A decrease in copy number will lead to decrease in concentration of bicoid protein. As a result, the posterior section will not have adequate amount of bicoid protein to express hunchback protein resulting in pattern B.
Answer 3. Pattern E
Increasing the copy number of bicoid protein will increase concentration of bicoid protein. As mutated hunchback protein contains only the low-affinity binding sites, it will uniformly binds throughout the body.
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