CBSE Class 10 Science 2022 · Paper 31/2/3 · Question 15

(a) All the F1 plants are tall with round seeds ($TtRr$), because tall and round are dominant (the parents being pure-breeding, as in Mendel's experiment). (b) A recessive trait is one that does not show in the F1 generation of a cross between pure parents with contrasting traits, being masked by the dominant trait; it shows only when both copies of the gene are recessive, and it reappears in F2. Here short height and wrinkled seeds are recessive. (c)(i) The new combinations (recombinant types, found in neither parent) are tall plants with wrinkled seeds and short plants with round seeds. The F2 ratio is tall round 9 : tall wrinkled 3 : short round 3 : short wrinkled 1, so the two new combinations appear in equal numbers, $3:3$, each $\frac{3}{16}$ of the plants. OR (c)(ii) (i) Tall with round seeds: $1600\times \frac{9}{16}=900$. (ii) Short with wrinkled seeds: $1600\times \frac{1}{16}=100$. Conclusion: height and seed shape are inherited independently of each other (and tall and round are dominant).