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IB Biology HL D3.2.10 Incomplete Dominance and Codominance Questions

Explain how both alleles can be expressed in codominance or produce an intermediate heterozygote, then analyse phenotype ratios in IB Biology HL D3.2.10.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Explain codominance as expression of both alleles in a heterozygote and incomplete dominance as an intermediate heterozygote phenotype.
  • Predict or interpret phenotype ratios from an incomplete-dominance cross, matching red, white and intermediate phenotypes to genotypes.
  • Predict or interpret codominant phenotype ratios from a heterozygote cross, including named feather phenotypes.

IB Biology HL D3.2.10 Incomplete Dominance and Codominance Questions question 1

[Maximum number: 1]

A variety of Pelargonium has yellow leaves. When plants of this variety are crossed, the resulting seeds produce green, yellow and white seedlings in the ratio 1: 2: 1. If plants with yellow leaves are crossed with plants with green leaves, what would the expected ratio of phenotypes in the offspring be?

Green

Yellow

White

1

2

1

3

1

0

2

2

0

2

1

1

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