Problem

Solutions For An Introduction to Genetic Analysis Chapter 4 Problem 46P

Step-by-Step Solution

Solution 1

Four alleles were used in an experiment on Arabidopsis thaliana. The allele “T” for presence of trichomes, “t” for absence of trichomes, “D” for tall plants, “d” for dwarf plants, “W” for waxy plants, “w” for non-waxy plants, “A” for presence of anthocyanin pigment, and “a” for absence of the pigment.

The T/t and D/d loci are linked with a distance of 26 m.u. apart on chromosome 1, while the W/w and A/a loci are linked with a distance of 8 m.u. apart on chromosome 2.

A pure double-homozygous recessive trichomeless nonwaxy plant is crossed with another pure double-homozygous recessive dwarf white plant.

a) The appearance of F₁ would be showing the presence of all the dominant phenotypes. The plant would show the presence of trichomes, tall, waxy cuticle, and the presence of the anthocyanin pigment.

Step #2 of 3

b) The chromosome 1 and 2 of the parents can be shown in this way:

The chromosome 1 and 2 of the F₁would be like this:

Step #3 of 3

c) If the F₁ progeny is testcrossed, the proportion of progeny, which will have all the four recessive phenotypes can be explained in the following way:

The progeny must inherit t d on chromosome 1 and w a recombinant chromosome 2 from the F₁ parent. Since the distance between t and d is 26 m.u. apart, the recombination frequency would be 26%. Half of these recombinant progeny [13%] would have the t d genotype.

Since the distance between w and a is 8 m.u. apart, the recombination frequency would be 8%. Half of these recombination progeny [4%] would have the w a genotype.

Since both of these are independent events, we multiply them: