Question

Drosophila has three linked autosomal genes that determine different traits. These genes are black (b), vestigial (vg), and singed(sn). Each of the three genes has two alleles: a dominant wild type allele, indicated by a "+" (plus) and a recessive mutant allele indicated by a "-" (minus). (These mutant alleles cause dark black spots, short "vestigial" wings, and bent "singed" hairs, respectively, when homozygous). A testcross is conducted between females that all have the same genotype and are triple heterozygotes for the three genes, and males that are all homozygous mutant for all three genes. Here are the numbers of progeny from the testcross, of each of the different possible phenotypes:

Progeny
Group     Phenotype       Number

   1 b+ vg - sn- 638

   2 b+ vg + sn- 2768

   3 b- vg + sn+ 621

   4 b+ vg + sn+ 9

   5 b+ vg-   sn+ 126

   6 b-   vg -   sn- 7

   7 b- vg + sn- 132

   8 b- vg - sn+ 2699

Total # progeny = 7000

A. From the data above, determine the genotype of the triple heterozygous females used in the testcross; in your genotype, be sure to include the proper order of the genes on the chromosomes. Indicate the genotype with a slash between the two homologous chromosomes

B. Type in three equations, numbered 1, 2, and 3. each with the proper numbers for calculating the genetic distances between the genes indicated

1. black (b) and vestigial (vg)

2. vestigial (vg) and singed (sn)

3. black (b) and singed (sn)

Answer 1