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A pure pea plant having round (R), yellow (Y) seeds is crossed with another pure pea plant having wrinkled (r), green (y) seeds. Subsequently F1 progeny is self-pollinated to obtain F2 progeny. (a) What do the seeds of F1 generation look like? (b) Give the possible combinations of traits in seeds of F2 generation. Also give their ratio. (c) State the reason of obtaining seeds of new combination of traits in F2 generation.

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(a) In the F1 generation, all seeds will be round and yellow, as round (R) and yellow (Y) are dominant traits. (b) F2 generation shows the following combinations: Round Yellow, Round Green, Wrinkled Yellow, Wrinkled Green, Ratio = 9 : 3 : 3 : 1 (c) In the F2 generation, new trait combinations appear due to the independent assortment of alleles during gamete formation.

class 10 science board exam paper 2026

CBSE Sample Paper Class 10 Science 2025-26

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1 Answer

  1. ANSWER: (a) All F₁ seeds are round and yellow. Genotype: RrYy.

    (b) Gametes from F₁: RY, Ry, rY, ry.
    F₂ phenotypes and ratio (from a 4×4 Punnett):

    • Round, Yellow = 9/16
    • Round, Green = 3/16
    • Wrinkled, Yellow = 3/16
    • Wrinkled, Green = 1/16

    (c) New trait combinations appear in F₂ because of independent assortment of the two gene pairs during meiosis (alleles for seed shape and seed colour segregate into gametes independently), producing recombinant genotypes and the 9:3:3:1 phenotypic ratio.

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