Let’s work through each part of the worksheet step by step.
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Problem 1: Cross between Hh (parent 1) and hh (parent 2)
Parent 1 gametes: H, h
Parent 2 gametes: h, h
Punnett Square:
| | h | h |
|---|---|---|
| H | Hh | Hh |
| h | hh | hh |
Frequencies:
- HH: 0
- Hh: 2 out of 4 → 50% or 2/4
- hh: 2 out of 4 → 50% or 2/4
Genotypes:
- P1: Hh and hh
- F1: Hh and hh (in equal proportions)
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Problem 2: Cross between AA (parent 1) and aa (parent 2)
Parent 1 gametes: A, A
Parent 2 gametes: a, a
Punnett Square:
| | a | a |
|---|---|---|
| A | Aa | Aa |
| A | Aa | Aa |
Frequencies:
- AA: 0
- Aa: 4 out of 4 → 100%
- aa: 0
Genotypes:
- P1: AA and aa
- F1: Aa (all offspring)
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Problem 3: Cross between Bb (parent 1) and Bb (parent 2)
Parent 1 gametes: B, b
Parent 2 gametes: B, b
Punnett Square:
| | B | b |
|---|---|---|
| B | BB | Bb |
| b | Bb | bb |
Frequencies:
- BB: 1 out of 4 → 25%
- Bb: 2 out of 4 → 50%
- bb: 1 out of 4 → 25%
Genotypes:
- P1: Bb and Bb
- F1: BB, Bb, bb (in 1:2:1 ratio)
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Problem 4: Tall (T) dominant over dwarf (t). Homozygous tall × homozygous dwarf
Homozygous tall = TT
Homozygous dwarf = tt
Cross: TT × tt
Punnett Square:
| | t | t |
|---|---|---|
| T | Tt | Tt |
| T | Tt | Tt |
P1 genotypes: TT and tt
F1 genotype(s): Tt (all)
F1 phenotype(s): All tall (since T is dominant)
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Problem 5: Cross two F1 from Problem 4 → Tt × Tt
Parent 1 gametes: T, t
Parent 2 gametes: T, t
Punnett Square:
| | T | t |
|---|---|---|
| T | TT | Tt |
| t | Tt | tt |
F1 genotypes (from problem 4): Tt
F2 genotype(s): TT, Tt, tt (in 1:2:1 ratio)
F2 phenotype(s): Tall (TT and Tt) and dwarf (tt) → 3 tall : 1 dwarf
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Final Answer:
1. Frequencies: HH=0, Hh=2/4, hh=2/4; Genotypes: P1=Hh & hh, F1=Hh & hh
2. Frequencies: AA=0, Aa=4/4, aa=0; Genotypes: P1=AA & aa, F1=Aa
3. Frequencies: BB=1/4, Bb=2/4, bb=1/4; Genotypes: P1=Bb & Bb, F1=BB, Bb, bb
4. Cross: TT × tt; P1 genotypes: TT, tt; F1 genotype: Tt; F1 phenotype: all tall
5. Cross: Tt × Tt; F1 genotypes: Tt; F2 genotypes: TT, Tt, tt; F2 phenotypes: 3 tall : 1 dwarf
Parent Tip: Review the logic above to help your child master the concept of punnett square worksheet 2 answer key.
