Solutions For An Introduction to Genetic Analysis Chapter 17 Problem 66P

These trisomic progeny are crossed to a diploid wild type plant.

Fr/fr/fr x fr/fr

Since only diploid progeny of the second cross are evaluated, if Fr is on the trisomic chromosome, the ratio of fast-to-slow ripening plants will be 1:2. Since diploid progeny of this cross will have one chromosome from each parent, the trisomic will also give only one chromosome to the progeny. Since the trisomic has three chromosomes, the probability of the Fr allele going into the progeny is 1:2.

Hence, the ratio of fast-to-slow ripening plants will also have the same ratio since they depend on the presence of the Fr allele.

b) If Fr is not located on the trisomic chromosome, the crosses would be simple as shown:

Fr/Fr x fr/fr

Or

Fr/fr x fr/fr

Hence, the ratio of fast-to-slow ripening plants will be 1:1.

c) The results of the crosses are shown in the table below:

The Fr allele is on the 7^th chromosome. We can identify this by the 1:2 ratio seen only in this chromosome. The other ratios do not match the 1:2 ratio.