CAIE A Level Biology 9700 · Inheritance
A non-consanguineous couple, both with normal pigmentation, have a child with oculocutaneous albinism (lack of melanin in skin, hair and eyes). Genetic analysis shows that the child is homozygous recessive for a mutation in the TYR gene.
Describe the relationship between the TYR gene, the enzyme tyrosinase, and the albino phenotype in this family.
5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.
Describe means: Say what happens or what something is like, in order and with detail. You are not being asked why. If there is data, quote it: name the trend, then give figures with units at the points where it changes.
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