Santosh loved his garden, especially his pea plants. One year, he noticed that all the pea plants he grew from one batch of seeds had round seeds. Curious, he took the seeds from one of those plants and grew a new generation. To his surprise, 75% of the new plants had round seeds, but 25% had wrinkled seeds.

(a) What were the genotypes of the parent plants that Santosh originally planted?

(b) Which trait is dominant – round or wrinkled seeds?

(c) What is the genotypic ratio of the second generation (F2) plants?

(a) The genotypes of the parent plants that Santosh originally planted were heterozygous dominant (Rr).
Since all plants in the first generation (F1) had round seeds, the parents must have been pure round-seeded (RR) and wrinkled-seeded (rr) plants. Crossing RR (round, homozygous dominant) × rr (wrinkled, homozygous recessive) produces all Rr (heterozygous round) plants in F1.

(b) Round seeds are dominant over wrinkled seeds, because the F1 plants (Rr) all show the round seed phenotype.

(c) 1:2:1