ConceptConceptDocsDocuments

CAIE IGCSE Biology 18.1.3 Discontinuous Variation

Practise recognising discontinuous variation as a limited set of distinct phenotypes with no intermediates.

Syllabus
2026–2028
Course
Biology 0610

Exam points

  • state that discontinuous variation has a limited number of phenotypes and no intermediates
  • identify ABO blood group, pea seed shape and pea seed colour as examples
  • use a category graph or table to distinguish discontinuous from continuous variation

18.1.3—Discontinuous variation results question 1

[Maximum number: 3]

A scientist investigated the inheritance of fur colour in cats.

The gene for coat colour is located on the X chromosome. The gene has two alleles:
- B black
- b orange.

The X chromosome with the allele for black is represented by XB\mathbf{X}^{\mathbf{B}}.
The X chromosome with the allele for orange is Xb\mathbf{X}^{\mathbf{b}}.
A female cat can be a mixture of these colours, described as calico.
Fig. 3.1 shows the inheritance of this condition in a family of cats.

Fig. 3.1

Fig. 3.1

Coat colour in cats is an example of discontinuous variation.

Explain why coat colour is an example of discontinuous variation.

All question bank results loaded