A plant of genotype CCdd is crossed to a plant of genotype ccDD; the F₁offspring are then testcrossed to a ccdd plant. If the genes are on different chromosomes, what percentage of the offspring will be ccdd ? A) 10 B) 20 C) 25 D) 30 E) 50

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Quizplus · Accepted Answer

25% of the offspring will be ccdd. In the initial cross (CCdd x ccDD), all F1 offspring will be heterozygous (CcDd) for both traits since the genes are on different chromosomes and assort independently. When these F1 offspring (CcDd) are testcrossed with a ccdd plant, the offspring will show all possible combinations of the two genes due to independent assortment, resulting in a 1:1:1:1 ratio of genotypes (CcDd, Ccdd, ccDd, ccdd). Therefore, 25% of the offspring will have the ccdd genotype.

A Plant of Genotype CCdd Is Crossed to a Plant