Question

A corn plant is homozygous for a mutant allele that results in no pigment in the seed (ie. white). The mutant is caused by Ds insertion that often exits late in the seed development, when there is an active Ac element in the genome. If there is NO active Ac element the seeds of this plant will be:

A) No pigment (ie white)
B) pigmented all over
C) White with small spots of pigment
D) White with large sports of pigment
E) weakly pigmented

Answer 1

The corn plant with a homozygous mutant allele causing white seeds will remain white without an active Ac element to initiate the excision of the Ds element. Thus, the seeds will express no pigment if there is no active Ac element.

Step-by-step explanation:

The subject of this question is biology, specifically genetics and how they relate to the coloration of corn kernels. The question revolves around the interaction of the Ds (Dissociator) and Ac (Activator) elements in maize, first described by the renowned scientist Barbara McClintock.

The corn plant in question is homozygous for a mutant allele that results in no pigment (white seeds) due to the Ds insertion. If there is no active Ac element in the genome, the seeds will remain white, as the Ac element is required to enable the Ds element to exit and restore pigment production in cells. Therefore, the correct answer to the student's question is A) No pigment (white).

When an active Ac element is present, it can cause the Ds element to excise, sometimes resulting in cells that revert back to pigment production, which would create spots of color (mosaicism). Without an active Ac element, there is no excision of Ds, so the seeds remain unpigmented.