In Drosophila mutations in the genes Dumpy wings Dw sepia ey

In Drosophila, mutations in the genes Dumpy wings (Dw), sepia eyes (se), and shaven bristles (sv) leads to abnormal dumpy wings, sepia colored eyes, and abnormally bristled flies, respectively. A cross between true breeding wild type flies and true breeding flies that display the dumpy wing, sepia eyes, and shaven bristle phenotypes results in an F1 that have abnormal wings.

1) What are the expected genotypes if we cross F1 flies? What are the expected phenotypes ratios?

2) Your peers decide to do the same exact F1 cross. Of a total of 1,000 flies, they obtain 377 dumpy wing flies and, 142 dumpy wing and shaven bristle flies. Based on the expected phenotype ratios you obtained above, perform a chi-square test to make sure your expected ratios are in accordance with the observed values

Solution

1).

Assume that the genes coding for wild type phenotype are, D, E and B; and their recessive alleles are, d (abnormal dumpy wings), e (sepia eyes), b (abnormally bristled flies). It is assumed that the wild type alleles are completely dominant over the recessive alleles.

The parental cross (pure breeds) is,

DD EE BB* dd ee bb --à Dd Ee Bb (100% wild type) --à F1

Cross between F1 will produce the progeny with the following genotype and phenotypic ratios:

D_E_B_ (27/64, all wild type)

D_E_bb (9/64, abnormally bristled)

D_ee B_ (9/64, sepia eyes)

dd E_B_ (9/64, abnormal dumpy wings)

D_ eebb (3/64, sepia eyes, abnormally bristled)

ddee B_ (3/64, abnormal dumpy wings, sepia eyes, abnormally bristled)

dd E_bb (3/64), abnormal dumpy wings, abnormally bristled)

ddeebb (1/64), abnormal dumpy wings, sepia eyes, abnormally bristled flies)

Thus, the phenotypic ratio is, 27:9:9:9:3:3:3:1