Problem

Solutions For An Introduction to Genetic Analysis Chapter 4 Problem 23P

Step-by-Step Solution

Solution 1

Two different pure-breeding lines of corn were crossed to obtain a phenotypic wild F₁ plant. The F₁ plant is heterozygous, for three recessive alleles – an, for anther, br, for brachytic, and f, for fine. The F₁ plant was then crossed with a tester, which was homozygous recessive, for three genes under study.

The F₂ progeny phenotypes are:

• Anther – 355.

• Brachytic, fine – 339.

• Completely wild type – 88.

• Anther, brachytic, fine – 55.

• Fine – 21.

• Anther, brachytic – 17.

• Brachytic – 2.

• Anther, fine – 2.

Total: 879

a) The genotypes of the parental lines are:

an f ⁺ br ⁺ /an f ⁺ br ⁺ x an⁺ f br/an⁺ f br

Step #2 of 3

b) The gene order can be determined by comparing the two most frequent classes with the least frequent classes. The parental classes are the first two with large number of progeny. The least frequent is the last two classes.

Since, the gene in the middle flips with respect to the flanking genes, the gene order is an f br.

The gene distances can be calculated in the following way:

Distance between an - f :