Chapter 19, Problem 17P

Researchers have exploited Minute mutations in order to study the phenotypes associated with recessive lethal mutations (l^-) that decrease the rate of cell division and thus make only very tiny homozygous mutant clones that are difficult to analyze. Many different strains of Drosophila carry dominant loss-of-function Minute (M) mutations in a variety of genes encoding ribosomal protein subunits. The M genes are haploinsufficient; flies with only one wild-type M⁺ gene copy have a slower pace of cell division, and thus prolonged development and subtle morphological abnormalities.

To circumvent the tiny clone problem, researchers generate GFP-marked homozygous l^-/l^- clones that are also M⁺/M⁺, in flies that are l^-/l⁺ and M^-/M⁺. The loss of the Minute mutation only in cells within the clone gives the l^-/l^- cells a growth advantage over their neighbors, enabling the mutant clone to grow large enough to study. Diagram chromosomes that could be used to generate such clones.