Solutions For An Introduction to Genetic Analysis Chapter 4 Problem 42P

A rice breeder has a triple heterozygote, which has three dominant and three recessive alleles for the characteristics of albino flowers (al), brown awns (b), and fuzzy leaves (fu). This heterozygote was testcrossed with a homozygous recessive organism.

The progeny details are:

• 170 – wild type

• 150 – albino, brown, fuzzy

• 5 – brown

• 3 – albino, fuzzy

• 710 – albino

• 698 – brown, fuzzy

• 42 – fuzzy

• 38 – albino, brown

a) The data presented indicates that the genes are linked. Since the progeny ratio does not match the trihybrid ratio, the three genes are linked. The parental classes are the classes with the highest number of progeny. One is albino and the other is brown, fuzzy. The classes with the least number of progeny would be the ones with the double crossover events. By comparing the most common class with the least common class, the middle gene can be determined as fu.

Representing the progeny with the genotypes:

• 170 – al⁺ fu⁺ b⁺

• 150 – albino, brown, fuzzy – al fu b

• 5 – brown – al⁺ fu⁺ b

• 3 – albino, fuzzy – al fu b⁺

• 710 – albino – al fu⁺ b⁺

• 698 – brown, fuzzy – al⁺ fu b

• 42 – fuzzy – al⁺ fu b⁺

• 38 – albino, brown – al fu⁺ b

Number of genotypes between al – fu:

• al⁺ fu⁺ - 170+5

• al⁺ fu – 689+42

• al fu⁺ - 710+38

• al fu – 150+3

The recombinants would be the classes with the least number of progeny. Hence the number of recombinants would be:

Number of genotypes between fu – b:

• fu⁺ b⁺ - 710+170

• fu⁺ b– 38+5

• fu b⁺ - 42+3

• fu b – 698+150

The recombinants would be the classes with the least number of progeny. Hence the number of recombinants would be:

The map distance can be calculated in the following way:

Distance between al and fu:

Distance between fu and b:

The map distances can be shown as a diagram: