Heterozygous Individuals via Dominant-Recessive Inheritance

Steps:

• Assign genotypes: Blue-eyed individuals are bb (homozygous recessive); brown-eyed are BB or Bb.
• Identify blue-eyed offspring: Their parents must each contribute a b allele, so brown-eyed parents of blue-eyed children are Bb (heterozygous).
• Check family tree: Persons 3, 4, and 5 have brown eyes but produce blue-eyed offspring (e.g., 3 parents a blue-eyed child; 4 and 5 similarly).
• Confirm others: No blue-eyed offspring from 1, 2, 6, or 7 means they could be BB (not must be Bb).

Why C is correct:

• Persons 3, 4, and 5 express dominant brown but transmit recessive b to blue-eyed (bb) children, requiring Bb genotype per Mendel's law of segregation.

Why the others are wrong:

• A: 1 and 7 lack blue-eyed offspring, so could be BB.
• B: 2 and 6 lack blue-eyed offspring, so could be BB.
• D: Excludes 3, who must be Bb due to blue-eyed child.

Final answer: C