Final Answer:
III-3: homozygous recessive
II-1: heterozygous
I-1: homozygous dominant
II-4: heterozygous
1. This trait is recessive.
Explanation: Because two unaffected parents (II-3 and II-4) have an affected child (III-3), the trait must be recessive. If it were dominant, at least one parent would have to show the trait.
2. We know II-3 and II-4 are heterozygous because they are unaffected but passed the trait to their child. Since the trait is recessive, both parents must carry one copy of the recessive allele — so they are heterozygous.
3. For the eye color pedigree:
- The son has blue eyes (recessive), so his genotype is bb.
- Both parents have brown eyes (dominant), but since they have a blue-eyed son, they must each carry one b allele → both are Bb.
- The woman’s father had blue eyes (bb), so she must have gotten a b from him → confirms she is Bb. Her mother had brown eyes — could be BB or Bb.
- The man’s parents both had brown eyes — they could be BB or Bb; since he is Bb, at least one of them must be Bb.
- In the pedigree:
- Son = bb (certain)
- Both parents = Bb (certain)
- Woman’s father = bb (certain)
- Woman’s mother = B_ (could be BB or Bb — not certain)
- Man’s parents = B_ (each could be BB or Bb — not certain)
Parent Tip: Review the logic above to help your child master the concept of genetic pedigree worksheet.
