Fig. 1 shows a pedigree for a family attending a hospital genetics clinic. Some family members have a recessive inherited condition that affects the ability...
Question 1 Report
Fig. 1 shows a pedigree for a family attending a hospital genetics clinic. Some family members have a recessive inherited condition that affects the ability of blood cells to carry oxygen during exercise. A filled symbol represents a person with the condition. The clinic has confirmed that the allele causing the condition is recessive and is not sex-linked. A couple, labelled parents in generation III, ask about the possible genotypes of their future eggs and sperm. The nurse also explains that environmental factors such as temperature do not change the alleles a person inherited.
(a) Use Fig. 1 to state which sex is affected in generation II. [1]
(b) Suggest the genotype of an unaffected parent who has an affected child. Use A and a. [2]
(c) Describe why brothers and sisters can inherit different combinations of alleles from the same parents. [3]
Answer Details
Labelled answer diagram:
(a) The affected person in generation II is male. [1]
(b) An unaffected parent with an affected child is likely to have genotype \(Aa\). They are unaffected because \(A\) is dominant, but they must carry recessive allele \(a\) to pass it to the affected \(aa\) child. [2]
(c) During meiosis, chromosome pairs separate. Gametes receive different combinations of alleles through independent assortment. Fertilisation is random, so different sperm can fuse with different eggs, giving siblings different allele combinations. [3]
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