Solutions For An Introduction to Genetic Analysis Chapter 4 Problem 66P

A cross of +++/+++ x wse/wse is made. The F₁ obtained is crossed with a homozygous recessive organism in a testcross. Assuming no interference, the proportion of different genotypes can be calculated.

Since, w and s are 8 m.u. apart; crossing over occurs only 8% of the time. The remaining 92% of the time, crossing over does not occur. Similarly, as s and e are 14 m.u. apart, crossing over occurs only 14% of the time. The remaining 86% of the time, crossing over does not occur.

a) +++:

This is a parental genotype. The frequency of parentals can be calculated in this way:

Half of this number would be the frequency of the genotype +++. This can be shown as:

b) Wse:

This is a parental genotype. The frequency of parentals can be calculated in this way:

Half of this number would be the frequency of the genotype wse which is shown:

c) +se:

This genotype needs a crossover between w and s. The frequency that shows recombination between these two genes would be:

Half of this number would be the frequency of the genotype +se, shown as:

d) w++:

This genotype needs a crossover between w and s. The frequency that shows recombination between these two genes would be:

Half of this number would be the frequency of the genotype w++. This can be shown as:

e) ++e:

This genotype needs a crossover between s and e. The frequency that shows recombination between these two genes would be:

Half of this number would be the frequency of the genotype ++e, shown as:

f) ws+:

This genotype needs a crossover between s and e. The frequency that shows recombination between these two genes would be:

Half of this number would be the frequency of the genotype ws+, shown as:

g) w+e:

This genotype needs a crossover between w, s, and s and e. The frequency that shows recombination between these two genes would be:

Half of this number would be the frequency of the genotype w+e, shown as:

h) +s+:

This genotype needs a crossover between w, s, and s and e. The frequency that shows recombination between these two genes would be:

Half of this number would be the frequency of the genotype +s+, shown as: