Question

Please answer both the parts of the answer.

Sex determination in Drosophila is determined by the ratio of X chromosomes to autosomes (X to A ratio) and relies on the cascade of alternatively spliced factors, some of which are themselves regulators of alternative splicing. The splicing regulator Sxl resides at the top of this cascade. Whether active Sxl protein will be present or not is determined by the X to A ratio of an organism. If the ratio of X to A = 1, functional Sxl protein is produced. When the ratio of X to A = 0.5, no functional Sxl protein is produced. Functional Sxl is necessary for formation of the active product of the Tra gene, another regulator of splicing. Sxl contributes to the formation of active Tra product by binding to its transcript and repressing a particular splicing event. (4 pt)

a) What would be the resulting gender of the XY flies in which a functional Sxl gene is overexpressed from a non-native promoter – so that its expression no longer depends on the X to A ratio? Briefly explain your answer.

b) What about the gender of XX flies in which a Sxl-binding site in the Tra gene is mutated? Briefly explain your answer

Answer 1