Solutions For An Introduction to Genetic Analysis Chapter 17 Problem 51P

In corn, the allele Pr stands for green stems and pr stands for purple stems. A plant with the genotype pr/pr with standard chromosomes is crossed with a plant with the genotype Pr/Pr which is homozygous for a reciprocal translocation between chromosomes 2 and 5.

The F₁ progeny is semisterile and has the phenotype of Pr. A backcross of this plant with the parent pr/pr, gives the following progeny:

• 764 – semisterile Pr

• 145 – semisterile pr

• 186 – normal Pr

• 727 – normal pr

The breakpoint can be treated as a gene with two alleles. One allele gives normal fertility while the second gives semisterility. The progeny can be grouped as shown below:

Parentals:

• 764 – semisterile Pr

• 727 – normal pr

Recombinants:

• 145 – semisterile pr

• 186 – normal Pr

The total is 1822.

The map distance between the Pr locus and the translocation point can be calculated in this way: