What is the chance that a child will be a carrier when one parent is heterozygous for a trait and the other is homozygous dominant?
Solution
Correct Answer: Option B
When one parent is heterozygous for a trait (meaning they carry one dominant and one recessive allele, e.g., Aa) and the other parent is homozygous dominant (carrying two dominant alleles, e.g., AA), the possible genetic combinations for their child can be analyzed using a Punnett square.
- The heterozygous parent (Aa) can pass on either the dominant allele (A) or the recessive allele (a).
- The homozygous dominant parent (AA) can only pass on the dominant allele (A).
The resulting combinations for the child are:
- 50% chance of AA (homozygous dominant, not a carrier)
- 50% chance of Aa (heterozygous, carrier)
Since a carrier carries one copy of the recessive allele but does not express the trait, a child with the Aa genotype will be a carrier. Therefore, there is a 50% chance that the child will be a carrier.
In summary:
- Heterozygous parent genotype: Aa
- Homozygous dominant parent genotype: AA
- Child genotype possibilities: AA (50%), Aa (50%)
- Chance child is a carrier (Aa): 50%
This is why the correct answer is Option 2: 50%.
Reference: Genetics in Medicine, 7th Edition, Chapter 4, Page 112
- The heterozygous parent (Aa) can pass on either the dominant allele (A) or the recessive allele (a).
- The homozygous dominant parent (AA) can only pass on the dominant allele (A).
The resulting combinations for the child are:
- 50% chance of AA (homozygous dominant, not a carrier)
- 50% chance of Aa (heterozygous, carrier)
Since a carrier carries one copy of the recessive allele but does not express the trait, a child with the Aa genotype will be a carrier. Therefore, there is a 50% chance that the child will be a carrier.
In summary:
- Heterozygous parent genotype: Aa
- Homozygous dominant parent genotype: AA
- Child genotype possibilities: AA (50%), Aa (50%)
- Chance child is a carrier (Aa): 50%
This is why the correct answer is Option 2: 50%.
Reference: Genetics in Medicine, 7th Edition, Chapter 4, Page 112
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