In Drosophila, a recessive, temperature-sensitive mu tation in the transformer-2 (tra-2) gene on

step 1 Different chromosomes leads to independent assortment. So given male CN positive CN, ST positive

In Drosophila, a recessive, temperature-sensitive mu tation...

In Drosophila, a recessive, temperature-sensitive $\mathrm{mu}$ tation in the transformer-2 (tra-2) gene on chromosome 2 causes $\mathrm{XX}$ individuals raised at $29^{\circ} \mathrm{C}$ to be transformed into phenotypic males. At $16^{\circ} \mathrm{C}$, these individuals develop as normal females. The sex type of $\mathrm{XY}$ individuals is unaffected by the tra-2 mutation. Suppose you are given three true-breeding, unlabeled vials containing different strains of Drosophila, all raised at $16^{\circ} \mathrm{C}$. Two of the strains have white eyes, and one has red eyes. You are told that one of the white-eyed strains also carries the tra-2 mutation. Devise two different methods to determine which white-eyed strain has the tra-2 mutation. Is there a reason to prefer one method over the other?

Key Concepts

Temperature-Sensitive Mutations

These mutations exhibit a normal phenotype under one set of conditions (the permissive temperature) but manifest a mutant phenotype under a different set of conditions (the restrictive temperature). This property allows researchers to control when and how the gene’s function is altered, providing a useful tool for dissecting gene function and developmental processes.

Drosophila Sex Determination

In Drosophila, sex determination is largely governed by the ratio of X chromosomes to autosomes, with specific genes, such as those in the transformer pathway, playing key roles. Mutations in genes involved in this pathway can lead to sex transformations, a phenomenon that helps elucidate the molecular mechanisms underlying sexual development.

Genetic Crosses and Phenotypic Markers

Using visible markers, such as eye color, permits the tracking of different genetic strains in crossing experiments. Such markers allow geneticists to correlate specific genotypes with phenotypes in offspring, thereby facilitating the identification of individuals carrying particular mutations or genetic traits.

Experimental Design in Genetics

Designing experiments that compare different strains under varying conditions (such as temperature shifts or reciprocal crosses) is critical for determining the presence and effect of specific mutations. Careful control and variation of experimental parameters enable the isolation of genetic factors influencing phenotype and improve the reliability of conclusions drawn from genetic analyses.

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