Assume that in corn, the kernels are purple, because of a dominant purple gene.
ID: 46108 • Letter: A
Question
Assume that in corn, the kernels are purple, because of a dominant purple gene. If a Ds element disrupts the gene, a recessive mutation is formed, and in homozygotes the kernels are clear. In heterozygotes, the cells are purple. A strain of corn, is homozygous for this mutation, and contains no Ac elements. This strain is mated with a homozygous purple plant that is homozygous for the Ac element that is located on another chromosome. The offspring of the F1 are allowed to self-mate. What ratio of purple: spotted: clear you expect in the F2 generation:
A. 2:1:1
B. 9:3:4
C. 12:3:1
D. 12:1:3
E. 9:4:3
Explanation / Answer
C. 12:3:1. because F2 plant can be either homozygous / heterozygous for the Ds element, so the phenotype associated with the insertion could either be present in every F3 plant (in the case of a F2 homozygote) or segregate 3:1 normal to mutant (if the F2 plant was heterozygous and the mutation is recessive).