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IB Biology HL D3.2.5 Dominant and Recessive Alleles Questions

Apply dominant and recessive allele rules to interpret heterozygous expression, genetic probabilities and offspring phenotypes in IB Biology HL D3.2.5.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Explain that a dominant allele is expressed in a heterozygote, while a recessive allele is expressed when no dominant allele masks it.
  • Calculate dominant/recessive genotype or phenotype probabilities from heterozygous parents, including lethal-dominant outcomes and inherited disorders.
  • Infer an unknown genotype or dominance relationship from a test-cross or observed offspring phenotype result.

IB Biology HL D3.2.5 Dominant and Recessive Alleles Questions question 1

[Maximum number: 1]

Huntington's disease is an autosomal dominant genetic disease. What are the chances of two parents that are heterozygous for the gene having a child with Huntington's disease?

A

25 %

B

50 %

C

75 %

D

100 %

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