If the first child of a couple was without dimples, an recessive trait, what is the chance that the second child will be born without dimples?
A) 100%
B) 25%
C) 50%
D) Cannot be determined from the phenotype of the child
If dimples (d) is a recessive trait to non-dimples (N), then each parent could be NN or Nd. If one or both NN, P(N) = 100%. If both Nd, then P(N) = 75%. Thus it cannot be determined from the phenotype of the first child.
To determine the chance that the second child will be born without dimples, we need to consider the parents' genotypes.
If the first child does not have dimples, which is a recessive trait, this means they must have received two copies of the non-dimple allele (dd) from each parent.
Since dimples are a recessive trait, the parents could both be carriers or have one copy of the dimple allele (Dd) and one copy of the non-dimple allele (dd).
Let's consider the possible scenarios for the parents' genotypes:
1. If both parents are carriers (Dd x Dd), there is a 25% chance that the second child will inherit two copies of the non-dimple allele (dd) and therefore be born without dimples.
2. If one parent is a carrier (Dd) and the other is a non-carrier (dd), there is a 50% chance that the second child will inherit one copy of the non-dimple allele (dd), and therefore be born without dimples.
3. If both parents are non-carriers (dd x dd), there is a 100% chance that the second child will also be born without dimples, as both parents can only pass down the non-dimple allele (dd).
Considering these possibilities, the correct answer is C) 50%, as this accounts for both scenarios 1 and 2.