A-LevelBiologyInherited change9700/42 · Feb/Mar 2018 · Q611 Marks

The black pigment melanin, which contributes to hair, skin and eye colour, is produced by cells known as melanocytes.

(a)(i)Outline how a gene mutation may occur.[4]
(a)(ii)Albinism is an autosomal recessive condition. Explain what is meant by the term recessive.[1]
(a)(iii)Using appropriate symbols, draw a genetic diagram to show how a man and a woman, who both produce melanin, could have a child with albinism.[3]
(b)Suggest how the starfish extract affects the activity of tyrosinase.[3]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2018). The mark or mark type is shown in brackets.

[4] any four from:
1 random / spontaneous ;
2 change in, base / nucleotide, sequence of DNA;
3 ref. to base, substitution / deletion / addition;
4 ref. to frame shift / AW ;
5 AVP; e.g. mutagens / UV light / ionising radiation
[1] allele only expressed, when a dominant allele not present / in a homozygote or allele not expressed in a heterozygote ;
[3] symbols explained ;
e.g. A = allele for, melanin production / normal pigment a = allele for, no melanin production / albinism
parental genotypes ;
e.g. Aa and Aa
offspring genotypes identifying child with albinism as aa ;
e.g. (AA Aa Aa) aa
[3] any three from:
1 the greater the concentration of extract, the lower the activity of tyrosinase ;
A inversely proportional
2 extract acts as an inhibitor / enzyme inhibited;
3 binds to, active site / allosteric site, (of tyrosinase) ;
4 ref. to alters pH ;
5 extract denatures tyrosinase ;

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