Some Hard Genetics Problems
1. In a series of two-point mapping crosses involving five
genes located on chromosome 2 (pr, adp, vg, c and b) in
Drosophila the following recombinant (single crossover)
frequencies were observed:
pr-adp 29% adp-c 8
pr-vg 13 adp-vg 16
pr-c 21 vg-b 19
pr-b 6 vg-c 8
adp-b 35 c-b 27
Given that the adp gene is near the end of the
chromosome, construct a map of these genes.
2. Pseudohypertrophic muscular dystrophy is an inherited
disorder that causes gradual deteriorationof the muscles. It
is seen almost exclusively in boysborn to normal parents,
and usually results in death in the early teens.
a) Is this disorder caused by a dominant or
b) Is its inheritance sex-linked or autosomal?
c) How do you know?
d) Why is this disorder almost never seen in girls?
3. Two hypothetical autosomal genes S (spotted) and B
(banded) give salamanders spotted or banded patterns as a
test cross, a double recessive salamanderis crossed with a
double heterozygote. Predict the phenotypic ratios under
the following conditions:
a) S and B are located on separate chromosomes
b) S and B are linked on the same autosome, but are so