DP Biology (first assessment 2025)

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Question SPM.2.SL.TZ0.b

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Date May Specimen-2023 Marks available [Maximum mark: 4] Reference code SPM.2.SL.TZ0.b
Level SL Paper 2 Time zone TZ0
Command term Outline Question number b Adapted from N/A
b.
[Maximum mark: 4]
SPM.2.SL.TZ0.b

Outline one example of a human disease caused by an autosomal recessive allele.

[4]

Markscheme
  1.  name of condition e.g. PKU / other example;
  2.  mutation in the gene for (the enzyme) phenylalanine hydroxylase (PAH) / if other example used name of gene that is mutated;
  3.  outline of inheritance pattern, e.g. both parents need to carry the recessive allele;
  4.  (without dietary modification, result is) toxic build-up of phenylalanine in the blood / low levels of tyrosine / symptoms if other example used;
  5.  phenylalanine is not converted to tyrosine (by the enzyme) / effect of the mutation on the protein/enzyme/metabolism if other example used;
  6.  requires dietary modification (as treatment) / treatment for other example used;

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