2. Imagine that you observe the following mutants in Drosophila. Based on the ph

Question

2. Imagine that you observe the following mutants in Drosophila. Based on the phenotype and inheritance described, assign each mutant into one of the following categories: maternal effect gene gap gene, pair-rule gene, segment polarity gene, or homeotic gene. (10 points each, 50 total) a. In homozygotes, larval embryos fail to develop. At death, wing, leg, heart, and gut primordia are present in duplicates with miror-image orientations b. Homozygous females are normal but produce larvae that have a head at each end and no caudal structures. Homozygous males are normal and have normal offspring. c. Homozygotes have shortened abdomens, missing segments Al through A4. d. Affected flies have halteres growing where their eyes should be. Da e. Homozygous embryos lack parasegments 2, 4, 6, 8, 10, 12, and 14.

Explanation / Answer

A. Segment polarity gene- in this case , the embryo fails to develop but at the final stage as here wing, leg, heart and gut premordia are present in duplicates with mirror image. And segment polarity genes come into the picture at the last stage of embryogenesis.

B. Maternal effect gene- maternal effect genes encodes for the proteins that are expressed even before the zygotic genes are expressed and are affected by mother genotype other than environment and irrespective of their own genotype. The anterior posterior axis pattern is decided before the fertilization of egg. This case shows head at both ends (anterior posterior axis pattern) and no caudal structure. Hence this is a kind of maternal affect gene mutation.

C. Gap gene In this case there are missing segments. Gap Gene are those whose mutation affect the formation of contiguous segments. So it's mutation will show deleted segments.

D. Homeotic gene- regulate anatomical structures.

E. Pair rule gene - pair rule genes are expressed in alternate parasegments and it's mutation affect likewise. In this case, even segments are deleted. Hence it is pair rule gene mutation.

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