Question

Explain how loss-of-function mutations in the following categories of genes would affect the morphologies of Drosophila larvae: A. Gap genes B. Pair-rule genes C. Segment-polarity genes

Short answer

Loss-of-function mutations in developmental genes would significantly impact Drosophila larvae morphologies: mutations in gap genes would result in missing large sections of body plan, mutations in pair-rule genes would lead to missing alternate segments, and mutations in segment-polarity genes would cause incorrect anterior-posterior orientation in each segment.

Step-by-step solution

Discuss the Function and Mutation Effects of Gap Genes

Gap genes are regulatory genes responsible for setting up the broad subdivisions along the anterior-posterior axis (head to tail axis) of the embryo. They are so named because when mutated, large 'gaps' of multiple missing segments appear in the embryo. Hence a loss-of-function mutation in gap genes would result in defects in the ordering and spacing of segments. In the larvae, large sections of the body plan would be missing.

Discuss the Function and Mutation Effects of Pair-rule Genes

Pair-rule genes are responsible for establishing the repeated, segmental units of the body along the anterior-posterior axis. They establish the organization of these segments. A loss-of-function mutation in these genes would result in the embryos missing alternate segments, thus the larvae would have a 'double segment' periodicity.

Discuss the Function and Mutation Effects of Segment-Polarity Genes

Segment-polarity genes are responsible for defining the anterior and posterior components of each segment. When there is a loss-of-function mutation in these genes, the embryos show mirror-image duplications of parts of each segment. This means that larvae would have incorrect anterior-posterior orientation in each segment.