In cats, the allele for short fur (F) is dominant over the allele for long fur (f). Two cats, both with short fur, are bred together. Explain why some of their offspring have long fur.

Eduqas GCSE Biology — 2.3.2 Inheritance · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Both parents are heterozygous (Ff). Each parent can pass either the F or the f allele to the offspring. If an offspring inherits the f allele from both parents (ff genotype), the dominant F allele is absent and the recessive f allele is expressed, giving long fur.

Examiner tips

  • State that both parents are heterozygous (Ff).
  • Explain that each parent can contribute either allele.
  • Show that an ff genotype results in long fur.
  • Mention that long fur is recessive and only appears when no F allele is present.

Common mistakes

  • Assuming both parents are homozygous dominant (FF).
  • Failing to explain that long fur is recessive.
  • Not linking the ff genotype to the expression of long fur.

Mark scheme (4 marks)

  1. Both parent cats are heterozygous (Ff)
  2. Each parent can pass on either the F allele or the f allele to offspring
  3. Offspring can inherit the f allele from both parents (ff genotype)
  4. Long fur is a recessive trait / the f allele is only expressed when no dominant allele is present

Key terms in this question

allele · dominant

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