In humans, the allele for brown eyes is dominant, and the allele for blue eyes is recessive. Based on Mendel’s principles of heredity, is it possible for two parents with brown eyes to have a child with blue eyes?

Question

Yes, because one parent could pass an allele for blue eyes to the child.
No, because one parent will always pass the dominant gene to the child.
Yes, because both parents could pass an allele for blue eyes to the child.
No, because both parents will pass the dominant allele for brown eyes to their child.

Answer 1

Yes, because both parents could pass an allele for blue eyes to the child.

In genetics, the brown eye allele (B) is dominant over the blue eye allele (b). If both parents have brown eyes, they could either have a genotype of BB (homozygous dominant) or Bb (heterozygous).

1. If both parents are Bb, there is a chance they could pass the recessive blue eye allele (b) to their child. The possible combinations for their offspring would be:
   • BB (brown eyes)
   • Bb (brown eyes)
   • Bb (brown eyes)
   • bb (blue eyes)

In this case, there is a 25% chance of having a child with blue eyes (bb).

2. If one parent is BB and the other is Bb, then all children would have at least one dominant allele (B) and thus will have brown eyes.

So, it is indeed possible for two parents with brown eyes to have a child with blue eyes if both parents carry the recessive allele for blue eyes (i.e., if both are Bb).