Punnett Square Practice or Quiz PDF with Answer Key - Laney Lee - Free Printable

Let’s go through each problem one by one. I’ll solve them step by step so you can understand how Punnett squares work and what the answers mean.

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Problem 1: Pea plant with genotype Bb

Genotype = Bb
This means one dominant allele (B) and one recessive allele (b).

Words that describe this:
- Heterozygous → YES (different alleles)
- Homozygous → NO (same alleles only)
- True breeding → NO (true breeding means homozygous — always passes same trait)
- Purebred → NO (same as true breeding)
- Hybrid → YES (another word for heterozygous)

✔ Circle: A. Heterozygous, E. Hybrid

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Problem 2: Rabbit with genotype AA

Genotype = AA → both alleles are the same and dominant.

Words that describe this:
- Heterozygous → NO
- Homozygous → YES
- True breeding → YES (will always pass on A)
- Purebred → YES (same as true breeding)
- Hybrid → NO

✔ Circle: B. Homozygous, C. True breeding, D. Purebred

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Problem 3: Purple flowers dominant to white. List all possible genotypes for purple flower.

Purple is dominant → so any genotype with at least one “P” will be purple.

Possible genotypes:
- PP → homozygous dominant → purple
- Pp → heterozygous → purple

White would be pp → but we’re asked for purple only.

✔ Answer: PP, Pp

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Problem 4: Yellow peas dominant to green. List all possible genotypes for green pea.

Green is recessive → only shows up if NO dominant allele is present.

So only genotype: pp (if we use Y/y, then yy)

Assuming standard notation: let’s say Y = yellow (dominant), y = green (recessive)

Then green pea must be: yy

✔ Answer: yy

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Problem 5: Tallness dominant to short. Tell phenotype for each genotype.

T = tall (dominant), t = short (recessive)

- TT → two dominants → tall
- Tt → one dominant → still tall (dominant masks recessive)
- tt → no dominant → short

✔ Answers:
TT → tall
Tt → tall
tt → short

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Problem 6: Grey fur dog (Gg) crossed with black fur dog (gg)

Grey is dominant? Wait — the problem says:

> A grey fur dog (Gg) is crossed with a black fur dog (gg).
> Complete the Punnett Square...

It implies G = grey (dominant), g = black (recessive) — because Gg is grey, gg is black.

Parent 1: Gg → gametes: G or g
Parent 2: gg → gametes: g or g

Punnett Square:

| | g | g |
|-------|-------|-------|
| G | Gg | Gg |
| g | gg | gg |

Offspring genotypes:
- Gg → 2 out of 4 → 50%
- gg → 2 out of 4 → 50%

Phenotypes:
- Gg → grey fur
- gg → black fur

✔ Genotypes: Gg, gg
✔ Phenotypes: grey fur, black fur

(You can write it as:
GENOTYPES: Gg - 50%, gg - 50%
PHENOTYPES: grey fur - 50%, black fur - 50%)

But since the worksheet just says “list all possible”, listing them is fine.

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Problem 7: Two hybrid grey dogs crossed (Gg x Gg)

Hybrid = heterozygous = Gg

Cross: Gg x Gg

Gametes from each parent: G or g

Punnett Square:

| | G | g |
|-------|-------|-------|
| G | GG | Gg |
| g | Gg | gg |

Genotypes:
- GG → 1/4
- Gg → 2/4
- gg → 1/4

Phenotypes:
- GG → grey
- Gg → grey
- gg → black

So:
Grey fur: GG + Gg = 3/4
Black fur: gg = 1/4

✔ Genotypes: GG, Gg, gg
✔ Phenotypes: grey fur, black fur

(Again, list all possible — not necessarily percentages unless asked.)

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Now moving to the right side of the worksheet.

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Problem 8: Two heterozygous curly haired guinea pigs crossed. Straight hair is recessive.

Curly is dominant? Let’s assume:

Let C = curly (dominant), c = straight (recessive)

Heterozygous = Cc

Cross: Cc x Cc

Punnett Square:

| | C | c |
|-------|-------|-------|
| C | CC | Cc |
| c | Cc | cc |

Genotypes:
- CC → 1/4
- Cc → 2/4
- cc → 1/4

Phenotypes:
- CC → curly
- Cc → curly
- cc → straight

✔ GENOTYPES: CC, Cc, cc
✔ PHENOTYPES: curly hair, straight hair

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Problem 9: Purebred red flower crossed with purebred white flower. Red is dominant.

Purebred red = RR
Purebred white = rr (since white is recessive)

Cross: RR x rr

All offspring get R from first parent, r from second → all Rr

Phenotype: all red (since R is dominant)

✔ GENOTYPES: Rr (only one possibility)
✔ PHENOTYPES: red flowers (all offspring)

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Problem 10: Heterozygous tall pea plant crossed with homozygous short pea plant.

Tall dominant → T
Short recessive → t

Heterozygous tall = Tt
Homozygous short = tt

Cross: Tt x tt

Gametes:
- Tt → T or t
- tt → t or t

Punnett Square:

| | t | t |
|-------|-------|-------|
| T | Tt | Tt |
| t | tt | tt |

Genotypes:
- Tt → 2/4
- tt → 2/4

Phenotypes:
- Tt → tall
- tt → short

✔ GENOTYPES: Tt, tt
✔ PHENOTYPES: tall, short

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Problem 11: Parents concerned about baby with blonde hair. Mother homozygous brown, father heterozygous brown. Some family members have blonde hair. Did hospital make mistake?

First, assign letters.

Brown hair is dominant → let’s say B = brown, b = blonde (recessive)

Mother: homozygous brown → BB
Father: heterozygous brown → Bb

Cross: BB x Bb

Gametes:
- Mother: B only
- Father: B or b

Punnett Square:

| | B | b |
|-------|-------|-------|
| B | BB | Bb |
| B | BB | Bb |

All offspring: either BB or Bb → both have at least one B → all should have brown hair

Blonde hair requires bb → which is impossible here, because mother gives only B.

So baby has blonde hair → genotype must be bb → but neither parent can give two b’s.

Mother is BB → can only give B
Father is Bb → can give B or b → so child could be BB or Bb → never bb.

Therefore, it’s genetically impossible for these parents to have a blonde-haired child.

✔ So yes — the hospital likely made a mistake (or there’s another explanation like adoption, mutation, etc., but based on genetics given, it shouldn’t happen).

Answer: Yes, the hospital probably made a mistake because two brown-haired parents (one homozygous, one heterozygous) cannot produce a blonde-haired child under normal Mendelian inheritance.

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Final Answer Summary:

Left Side:

1. A pea plant has genotype Bb → circle: Heterozygous, Hybrid
2. Rabbit has genotype AA → circle: Homozygous, True breeding, Purebred
3. Purple flower genotypes: PP, Pp
4. Green pea genotype: yy (or pp, depending on letter used — but typically yy for yellow/green)
5. Phenotypes:
- TT → tall
- Tt → tall
- tt → short
6. Grey (Gg) x Black (gg):
- Genotypes: Gg, gg
- Phenotypes: grey fur, black fur
7. Hybrid grey x hybrid grey (Gg x Gg):
- Genotypes: GG, Gg, gg
- Phenotypes: grey fur, black fur

Right Side:

8. Curly (Cc) x Curly (Cc):
- Genotypes: CC, Cc, cc
- Phenotypes: curly hair, straight hair
9. Red (RR) x White (rr):
- Genotypes: Rr
- Phenotypes: red flowers
10. Tall (Tt) x Short (tt):
- Genotypes: Tt, tt
- Phenotypes: tall, short
11. Baby with blonde hair from BB mom and Bb dad → Yes, hospital likely made a mistake — impossible under given genetics.

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Final Answer:
See above detailed solutions for each question. All answers follow Mendelian genetics rules using Punnett squares. For the last question, the answer is yes, the hospital likely made a mistake because the parents’ genotypes cannot produce a blonde-haired child.