Detached ear lobes is a dominant trait that is controlled by one gene, where the recessive allele is attached ear lobes.
If a person who is heterozygous to the trait has a child with a person who has attached ear lobes, what will be the phenotypic proportions of the offspring?
The heterozygous individual has one dominant allele (D) for detached ear lobes and one recessive allele (d) for attached ear lobes. The person with attached ear lobes has two recessive alleles (dd).
When these two individuals have a child, the possible genetic combinations are:
1) DD x dd (detached ear lobe parent passes on the dominant allele)
Offspring: All offspring will have detached ear lobes (100% phenotypic proportion)
2) Dd x dd (detached ear lobe parent passes on either the dominant or recessive allele)
Offspring: 50% will have detached ear lobes (Dd), and 50% will have attached ear lobes (dd)
Therefore, the phenotypic proportions of the offspring will be:
- 100% detached ear lobes if the heterozygous individual passes on the dominant allele.
- 50% detached ear lobes and 50% attached ear lobes if the heterozygous individual passes on the recessive allele.