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?

Pink

The correct answer is Option (3)- Pink

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. When the F1 was self-pollinated the F2 resulted in the following ratio 1 (RR) Red : 2 (Rr) Pink : 1 (rr) White.

Here the genotype ratios were exactly as we would expect in any mendelian monohybrid cross, but the phenotype ratios had changed from the 3:1 dominant : recessive ratio. What happened was that R was not completely dominant over r and this made it possible to  distinguish Rr as pink from RR (red) and rr (white) .

 Results of monohybrid cross in the plant Snapdragon, where one allele is incompletely dominant over the other allele.