In a certain family, a disorder is autosomal dominant (allele D) and appears in every generation. Two affected individuals, both known to be heterozygous (Dd), have four children. How many of the children are expected to be affected by the disorder?
Answer
Three out of four children (75%)
The correct answer is Three out of four children (75%) — Therefore, out of four children, three are expected to be affected.
Step-by-step solution
- Write the genotype of each parent: Dd × Dd.
- Create a Punnett square with gametes D and d from each parent.
- The square yields genotypes: DD, Dd, Dd, dd.
- Identify the affected genotypes: DD, Dd, and Dd (three out of four).
- Calculate the proportion: 3/4 = 0.75 = 75%.
- Therefore, out of four children, three are expected to be affected.
Common mistake: Assuming a 50% chance because only one dominant allele is needed, forgetting the DD genotype.
Concept tested: Autosomal dominant inheritance – heterozygous cross
Published · How this solution was prepared and checked
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