Drosophila eyes are normally red Several purpleeyed strains

Drosophila eyes are normally red. Several purple-eyed strains have been isolated as spontaneous mutants, and the purple phenotype is autosomal recessive in each case. To investigate allelism between these different purple mutations, two purple-eyed pure strains were crossed. the purple mutations are in different genes(i.e., they are not allelic), the phenotypic ratios in the F1 are expected to be: 100% red 75% red: 25% purple 50% red: 50% purple 25% red: 75% purple 100% purple

Solution

1. In autosomal recessive two copies of an abnormal gene must be present in order for the trait to develop.

2. So two purple-eyed pure strains will have two copies of abnormal gene in each parent.

3. If two purple-eyed pure strains have crossed all the progeny would be purple (100%) in case they are allelic.

4. If they are not allelic they phenotypic ratio would 75% red and 25% purple.

5. Becuase red eyes are soma, and genes are germplasm, they cannot be equated.

6.Chemical stydies of the eye pigments revealed pteridine compound produced in biosynthetic series.

7. It is hypothesized that each mutant involves a block or deviation at a particular step in a biosynthetic series.

8. So white is the failure at the beginning, purple is failure in the meddile of biosynthetic series. Red is the produced if sucess at all steps.