Question

Why are $F_2$ phenotypic and genotypic ratios same in a cross between red-flowered Snapdragon and white flowered Snapdragon plants ? Explain with the help of a cross.

Answer 1

In snapdragon (Antirrhinum anus) the cross between a red-flowered plant (RR) and a white-flowered plant (rr) results in all pink flowered (Rr) plants in the F1 generation. A self-cross between two F1 plants results in red, pink and white flowers in the ratio of 1:2:1. The genotype of the resulting plants is also in the ratio of 1:2:1 for RR (red), Rr (pink) and rr (white) flowered plants. The cross can be shown as in the image. This is called incomplete dominance. Due to this reason, the F${}_2$ phenotypic ratio and genotypic ratios are same in a cross between red-flowered and white flowered snapdragon plants.