Biology Inheritance / Variation & Genetics ETEA 2023
PMDC Verified Question 36 of 94
When round and yellow color seeded plant (RrYy) is self-crossed the number of plants with round and yellow color seeds obtained is ____ in 32 plants.
A
18
B
9
C
3
D
1
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: 18
Concept:

A standard dihybrid cross of two heterozygotes yields a predictable 9:3:3:1 phenotypic ratio.

Solution:

  • The cross is RrYy x RrYy.
  • The proportion of offspring expressing both dominant traits (Round and Yellow) is 9/16.
  • To find the expected number in a specific population, multiply the fraction by the total number of plants:


$$ \text{Expected} = \frac{9}{16} \times 32 $$

$$ \text{Expected} = 9 \times 2 = 18 $$

  • Therefore, 18 plants out of 32 will have round and yellow seeds.


Why other options are incorrect:

  • 9: Is the numerator of the ratio, not the absolute number out of 32.
  • 3: Represents the proportion for single-dominant phenotypes (e.g., Round/Green).

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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