Question

In the mixed eosin stocks, you will be able to find a heterozygous female. How can you tell the female is heterozygous? Why does she look that way? What are her protein levels? How do they compare to the homozygous female and the hemizygous male? How do her protein levels relate to activity/function/phenotype?

Answer 1

The question pertains to the genetics of Drosophila (often known by its common name, fruit fly). It is a widely studied invertebrate model organism in the field of genetics. Several lines have been developed to address specific characters/traits. One such character is the eye color. In Drosophila, the eye color is X-linked. The gene has four alleles, which have uniques names based on the phenotype observed. These alleles are wild-type, eosin, apricot and white. The wild-type allele is dominant over all the alleles, while the white allele is recessive to all the alleles. Apricot and eosin are dominant over white but recessive over wild-type.

Since these genes are X-linked, the females possess two alleles while the males only have a single allele. This locus is known to exhibit what is called as the gene dosage effect. When two alleles are present at a locus that exhibit gene dosage effect, the total protein product produced comes 50% from each allele. Thus, in case of heterozygous female for eosin, 50% protein product would be eosin and the 50% protein product would be wild-type. In the case of homozygous female for eosin however, 100% protein would be eosin, thus the colour would be more deeper in the case of homozygous than the heterozygous females. Additionally, the males that have eosin allele, have only one copy of the gene and hence their 100% protein content comes from just one allele. Thus, the heterozygous females produce eosin at the same levels as the males that have eosin allele. Hence their eye colors are similar and less deep than that of homozygous females. This method is employed for selecting the heterozygous females from the stock.