Sam has dark hair, and Martha has blonde hair. Assume that Sam’s genotype is DD (two dominant genes for dark hair). Which of the following are possible if Sam and Martha have a child?

Question

A child with dark hair (DD)

A child with dark hair (Dd)
A child with blonde hair (Dd)
A child with blonde hair (dd)

Answer 1

To determine the possible genotypes and phenotypes of a child between Sam (genotype DD) and Martha (whose hair color is blonde and can be assumed to have the genotype dd based on typical inheritance patterns), we can analyze their genetic contributions.

Sam's genotype:

• DD (homozygous dominant for dark hair)

Martha's genotype:

• dd (homozygous recessive for blonde hair)

When they have a child, the possible genotypes can be determined from the parents' contributions:

• From Sam, the child will always inherit a D allele (since he is DD).
• From Martha, the child will always inherit a d allele (since she is dd).

Thus, the potential genotype of the child can only be:

• Dd

Based on this genotype, the phenotype of the child would be:

• Dark hair (because the D allele is dominant over the d allele).

Now, let's evaluate the options given:

1. A child with dark hair (DD) - Not possible (the child can only inherit Dd).
2. A child with dark hair (Dd) - Possible (this is the only possible genotype).
3. A child with blonde hair (Dd) - Not possible (the child must be Dd, which results in dark hair).
4. A child with blonde hair (dd) - Not possible (the child cannot inherit the dd genotype).

In summary, the only possible outcome for the child is:

• A child with dark hair (Dd).