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Huntington's disease is an autosomal dominant genetic disease - HSC - SSCE Biology - Question 25 - 2023 - Paper 1
Question 25
Huntington's disease is an autosomal dominant genetic disease. (a) Using the pedigree, justify the genotype of individual 'H'. In your answer, refer to the letters ... show full transcript
Worked Solution & Example Answer:Huntington's disease is an autosomal dominant genetic disease - HSC - SSCE Biology - Question 25 - 2023 - Paper 1
Step 1
Justify the genotype of individual 'H'
Answer
Individual 'H' must be heterozygous for Huntington's disease gene (genotype Hh). This conclusion arises because both of H's children (I and K) do not display Huntington's disease, while H's parents (II E and F) do have affected offspring. The presence of unaffected children indicates that H must carry one normal allele (h) alongside the Huntington's disease allele (H), as individuals with two dominant alleles (HH) would not produce unaffected offspring.
Step 2
Identify possible genotypes of autosomal dominant inheritance
Answer
In autosomal dominant inheritance, the potential genotypes include:
- Homozygous dominant (HH) - affected individuals.
- Heterozygous (Hh) - affected individuals, like H.
- Homozygous recessive (hh) - unaffected individuals. Since individuals I and K are unaffected, their genotype must be hh.
Step 3