When a snapdragon plant homozygous for red flower (RR) is crossed with another plant bearing white flowers, (rr) what colour will be observed in flowers of F1 generation?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Pink
In snapdragon, flower colour shows incomplete dominance: neither allele fully hides the other.
RR (red) × rr (white) → all F1 Rr, pink.
Option (1) Red — Incorrect. Red would need R to be fully dominant.
Option (2) White — Incorrect. White needs rr; every F1 plant has one R.
Option (3) Pink — Correct. Every F1 plant is Rr. In snapdragon, R is not completely dominant over r, so the F1 flowers are in between red and white, that is pink. This is incomplete dominance.
Option (4) Red and white — Incorrect. All F1 plants are alike (Rr); red and white reappear only in F2.
NCERT Extract:
Incomplete Dominance – “… When experiments on peas were repeated using other traits in other plants, it was found that sometimes the F1 had a phenotype that did not resemble either of the two parents and was in between the two. The inheritance of flower colour in the dog flower (snapdragon or Antirrhinum sp.) is a good example to understand incomplete dominance. In a cross between true-breeding red-flowered (RR) and true-breeding white-flowered plants (rr), the F1 (Rr) was pink (Figure 4.6).”