The loci for A and B are both located on the X chromosome of

The loci for A and B are both located on the X chromosome of Drosophila. A female of genotype AaBb is crossed to a wild AB male (A>a, B>b). The following progeny are obtained.

a) Why are the females all phenotypically AB

b) Is the linkage configuration of the parental female in coupling or repulsion? Why?

c) What is the map distance between the loci A and B?

d) The same parental female is crossed with an \'ab\' male. Predict the frequency and phenotypes of the offspring.

Solution

X^ABX^ab female X X^AB Ymale

X^ABX^AB : X^AB Y : X^AB X^ab : X^ab Y

Females are phenotypically AB because they have two X chromosomes. In this one dominant allele is sufficient for expression of the phenotype.

b) In parental female it is coupling

c) The distance is calculated by

distance = no. of recombinants / total * 100

= 82.8 cM is the distance between