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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' with reference to H's offspring
Answer
Individual 'H' must be heterozygous for the Huntington's disease gene (genotype Hh). This is evidenced by the fact that individual 'H' has children (I and K) that do not have Huntington's disease, and children that do have Huntington's disease (J and L). Therefore, 'H' must carry both the allele for Huntington's disease (H) and the normal allele (h) since she has both normal and affected children.
Step 2
Identify possible genotypes of autosomal dominant inheritance
Answer
The possible genotypes for an autosomal dominant trait like Huntington's disease include homozygous dominant (HH) and heterozygous (Hh). However, since individual 'H' has affected and unaffected offspring, she cannot be homozygous dominant (HH), as this would result in all offspring being affected.
Step 3
Provide some relevant information
Answer
In pedigrees, the presence of affected individuals among offspring typically indicates that one or both parents carry the dominant allele. In this case, the presence of unaffected children alongside affected children supports the conclusion that individual 'H' is heterozygous.