Genetics

The allele b gives Drosophila flies a black body and b + gives brown, the wild-type

phenotype. The allele wx of a separate gene gives waxy wings and wx + gives nonwaxy,

the wild-type phenotype. The allele cn of a third gene gives cinnabar eyes and

cn + gives red, the wild-type phenotype. A female heterozygous for these three genes is

testcrossed, and 1000 progeny are classified as follows:

5 wild type

6 black, waxy, cinnabar

69 waxy, cinnabar

67 black

382 cinnabar

379 black, waxy

48 waxy

44 black, cinnabar

a. Explain these numbers for each progeny class in terms of genetic linkage.

b. Draw the alleles in their proper positions on the chromosomes of the triple

heterozygote female used in the above testcross.

c. If it is appropriate according to your explanation, calculate interference.

d. If two triple heterozygotes of the type in this problem are crossed, what

proportion of progeny would be black, waxy? (Remember, there is no crossing-over in

Drosophila males.)

(I understand a. & b. but not c. and d; feel free to provide an approach. thank you)