Galactosaemia is a rare genetic disease in which the build-up of the monosaccharide galactose can result in an enlarged liver, kidney failure and brain damage. Galactose is produced in the body from the digestion of the sugar lactose, found in milk.
Galactosaemia is caused by a recessive mutation of the GALT gene. The normal dominant allele codes for an enzyme which converts galactose to glucose.
(b) If the phenotypes of parents are known, the probabilities of having a child with galactosaemia, an unaffected child (healthy, not a carrier) or a child who is a carrier can be calculated.
Complete Table 7.1 to show the results of these calculations.
[Table 7.1]

Q: What topic does this question test?

This question tests Inherited change in A-Level Biology (syllabus code 9700). It is worth 9 marks.

Q: Which exam paper is this question from?

This question appeared in the Cambridge A-Level Biology Oct/Nov 2017 examination, Paper 4 Variant 3 (9700_w17_qp_43.pdf).

Question

Galactosaemia is a rare genetic disease in which the build-up of the monosaccharide galactose can result in an enlarged liver, kidney failure and brain damage. Galactose is produced in the body from the digestion of the sugar lactose, found in milk.
Galactosaemia is caused by a recessive mutation of the GALT gene. The normal dominant allele codes for an enzyme which converts galactose to glucose.
(b) If the phenotypes of parents are known, the probabilities of having a child with galactosaemia, an unaffected child (healthy, not a carrier) or a child who is a carrier can be calculated.
Complete Table 7.1 to show the results of these calculations.
[Table 7.1]

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