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IB Biology SL D3.2.13 Pedigree Charts Questions

Use pedigree generations, affected phenotypes and sex-specific transmission to identify inheritance patterns and infer genotypes in IB Biology SL D3.2.13.

Syllabus
First assessment 2025
Course
Biology SL
Level
SL

Exam points

  • Read pedigree symbols and family generations to identify autosomal dominant, autosomal recessive or X-linked inheritance patterns.
  • Infer an individual genotype or calculate an inherited-disorder probability from the relationships and phenotypes shown in a pedigree.

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Study D3.2.13—Pedigree charts conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB Biology SL D3.2.13 Pedigree Charts Questions question 1

[Maximum number: 4]

Thrombophilia is a human genetic condition where the blood has an increased tendency to clot. The condition is caused by a single base substitution mutation in DNA. If a person is homozygous for the gene, they are at greater risk for developing a blood clot than an individual who is heterozygous. The pedigree chart shows the inheritance of thrombophilia in a family.

Figure for Question IB Biology SL D3.2.13 Pedigree Charts Questions question 1 — IB Biology SL

Question (a)

(a)

Draw the symbol for individual X on the diagram.

[ 1 ]

Question (b)

(b)

Calculate the probability of male Y having an allele for the disorder.

[ 1 ]

Question (c)

(c)

Explain how the information in the box labelled B indicates that the gene is not sex-linked.

[ 2 ]
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