In a particular plant, leaf colour is controlled by gene locus D. Plants with at least one allele D have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding, dark-leafed plant is crossed with a light-leafed one, and the F 1 offspring is allowed to self-pollinate. The predicted outcome of the F 2 is diagrammed in the Punnett square shown in the figure, where 1, 2, 3 and 4 represent the genotypes corresponding to each box within the square.
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Which of the boxes marked 1-4 correspond to plants that will be true-breeding?
A) 1 and 4 only
B) 2 and 3 only
C) 1, 2, 3 and 4
D) 1 only

Question

In a particular plant, leaf colour is controlled by gene locus D. Plants with at least one allele D have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding, dark-leafed plant is crossed with a light-leafed one, and the F 1 offspring is allowed to self-pollinate. The predicted outcome of the F 2 is diagrammed in the Punnett square shown in the figure, where 1, 2, 3 and 4 represent the genotypes corresponding to each box within the square. 
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Which of the boxes marked 1-4 correspond to plants that will be true-breeding?
A) 1 and 4 only 
B) 2 and 3 only 
C) 1, 2, 3 and 4 
D) 1 only

Quizplus · Accepted Answer

True-breeding plants are homozygous for the traits in question. Without specific genetic information about the plants in boxes 1-4, we can only assume that boxes 1 and 4 are true-breeding based on the given options.

In a Particular Plant, Leaf Colour Is Controlled by Gene