Question

1. Three of the many recessive mutations in Drosophila melanogaster that affect body color, wing shape, or bristle morphology are black (b) body, versus grey in the wild type; dumpy (dp), obliquely truncated wings, versus long wings in the wild type; and hooked (hk) bristles at the tip, versus non hooked bristles in the wild type. From a cross of a dumpy female with a black, hooked male, all the F1 were wild type for all three characters. The testcross of an F1 female with a dumpy, black, hooked male gave the following results:
wild type 169
black 19
black, hooked 301
dumpy, hooked 21
hooked 8
hooked, dumpy, black 172
dumpy, black 6
dumpy 304
______________________________________
Total 1,000
a. Show the order and give the map distances between the genes. Construct a genetic map of the linkage group (or groups) these genes occupy.
b. Determine the coefficient of coincidence for the portion of the chromosome involved in the cross. How much interference is there?

Answer 1

Answer:

(a)

First the parental cross is b+ hk+ dp/b+ hk+ dp female x b hk dp+/b hk dp+ male. The F1 testcross would be b+ hk+ dp/b hk dp+ female x b hk dp/b hk dp male.

Then the F2 generation would be given by the following table:

Phenotype

Gamete Genotype

Number

Class

dumpy

b + hk + dp

304

parental

black, hooked

b hk dp +

301

parental

hooked, dumpy, black

b hk dp

172

Single crossover

wild-type

b + hk + dp +

169

Single crossover

dumpy, hooked

b + hk dp

21

Single crossover

black

b hk + dp +

19

Single crossover

hooked

b + hk dp +

8

Double crossover

dumpy, black

b hk + dp

6

Double crossover