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CAIE IGCSE Biology 17.4.14 Codominance

Practise recognising codominance when both alleles in a heterozygous organism contribute to its phenotype.

Syllabus
2026–2028
Course
Biology 0610

Exam points

  • define codominance as both alleles contributing to the heterozygous phenotype
  • recognise a mixed or combined phenotype rather than complete dominance by one allele
  • interpret a heterozygote cross that gives a 1:2:1 phenotype ratio

17.4.14—Codominance as a situation in which question 1

[Maximum number: 1]

The plant Camellia japonica has flowers that can be white, red or a mixture of these two colours. When red-flowered plants are crossed with white-flowered plants, all the offspring plants have flowers with petals that are a mixture of red and white, as shown in Fig. 2.2.

Fig. 2.2

Fig. 2.2

- The gene for petal colour in C. japonica is given the symbol P.
- The allele for white petals is given the symbol PWW\mathbf{P W}^{\mathbf{W}}.
- The allele for red petals is given the symbol PRR\mathbf{P R}^{\mathbf{R}}.

State the type of inheritance that is shown by petal colour in C. japonica.

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