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CAIE IGCSE Biology 17.4.10 Interpreting Pedigree Diagrams

Practise using pedigree symbols and family relationships to infer affected status, inheritance pattern and possible genotypes.

Syllabus
2026–2028
Course
Biology 0610

Exam points

  • read circles, squares, shading and connecting lines using the pedigree key
  • infer dominant or recessive inheritance from affected and unaffected parents and offspring
  • deduce individuals who must be homozygous, heterozygous or carriers

17.4.10—Interpret pedigree diagrams question 1

[Maximum number: 1]

The eye is a sense organ that responds to light.
Fig. 4.1 is a diagram of a section through the human eye.

Fig. 4.1

Fig. 4.1

Some people inherit colour blindness and cannot identify certain colours, even in bright light. The gene responsible for colour vision is located on the X chromosome.

There are two alleles for this gene on the X chromosome:
- XB\mathrm{X}^{\mathrm{B}} - normal colour vision
- Xb\quad \mathrm{X}^{\mathrm{b}} - colour blindness.

Fig. 4.2 shows a pedigree diagram for colour blindness.

Fig. 4.2 shows a pedigree diagram for colour blindness.

Person 13 in Fig. 4.2 is male. His parents are person 7 and person 8.

Use the key to complete Fig. 4.2 by drawing the correct symbol for person 13.

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