Question Constellation Sign up for free

AQA · GCSE · Biology · Higher

AKU genetic cross probability

Q03.3 5 marks

AKU is a genetic disorder. Figure 3 shows the inheritance of AKU in one family.

Figure 3
Figure 3

Figure 3

Enlarged question image

Figure 3

A female who has AKU and a male who is heterozygous for AKU plan to have a child.

Determine the probability that the child will have AKU. You should:

  • complete Figure 4
  • identify the phenotype of each offspring genotype
  • use the symbols: A = dominant allele; a = recessive allele

Practice unavailable

This question can be viewed, but its original response format is not available for practice yet.

Write your answer first. You can study the marking guidance whenever you need it.

Study the marking See what earns credit and compare it with a full-mark answer.

Marking points

  1. 1 Enters female gametes a and a.
  2. 2 Enters male gametes A and a in either order.
  3. 3 Derives four offspring genotypes consistently from the parental gametes.
  4. 4 Assigns the correct AKU/no-AKU phenotype to each derived genotype.
  5. 5 States a probability that matches the completed cross.

Why this answer loses marks

I completed the genotype grid but did not identify which outcomes show the disorder.

The genotypes must be linked to phenotype before the probability can be justified from the matching outcomes.