GATE 2021 BT – Question 49
A homozygous round-yellow pea is crossed with a homozygous wrinkled-green pea. F1 intercross produces 560 F2 progeny. The number with both dominant traits is _______.
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Correct answer: 315
Explanation
This is a dihybrid cross: round-yellow ($RRYY$) × wrinkled-green ($rryy$) gives $RrYy$ in F1.
**F1 × F1** gives the classical F2 ratio of $9:3:3:1$:
- 9/16 round, yellow (both dominant),
- 3/16 round, green,
- 3/16 wrinkled, yellow,
- 1/16 wrinkled, green.
**Both dominant traits:**
$$560\times\frac9{16}=\mathbf{315}.$$