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 to fill in the Punnett squares and answer the questions.

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Problem 1: Pea plant with genotype Bb

Genotype = Bb
This means it has two different alleles → heterozygous
It is not purebred (purebred would be BB or bb) → so NOT true breeding, NOT purebred
Hybrid = same as heterozygous → YES

✔ Circle: A. Heterozygous, E. Hybrid

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Problem 2: Rabbit with genotype AA

Genotype = AA → both alleles same → homozygous
Also, since it’s two dominant alleles, it’s true breeding and purebred
Not hybrid (hybrid = mixed), not heterozygous

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

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Problem 3: Purple flowers dominant over white in peas

Purple is dominant → let’s say P = purple, p = white
Possible genotypes for purple flower: must have at least one P → PP or Pp

✔ Answer: PP, Pp

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Problem 4: Yellow peas dominant over green

Yellow = dominant (Y), green = recessive (y)
Green pea must be homozygous recessive → only yy shows green

✔ Answer: yy

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Problem 5: Tallness dominant over short in pea plants

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

- TT → tall (homozygous dominant)
- Tt → tall (heterozygous — still shows dominant trait)
- tt → short (only way to show recessive trait)

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

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

Grey = G (dominant), black = g (recessive)
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, Gg, gg, gg → so 2 Gg, 2 gg → ratio 1:1

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

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

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

Both parents: Gg → gametes: G or g each

Punnett Square:

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

Genotypes:
→ GG, Gg, Gg, gg → so 1 GG : 2 Gg : 1 gg

Phenotypes:
→ GG = grey
→ Gg = grey
→ gg = black
So 3 grey : 1 black

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

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Problem 8: Two heterozygous curly haired guinea pigs crossed

Curly hair = ? Wait — problem says “straight hair is recessive” → so curly is dominant!

Let’s define:
C = curly (dominant)
c = straight (recessive)

Parents: both heterozygous → Cc x Cc

Punnett Square:

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

Genotypes: CC, Cc, Cc, cc → 1 CC : 2 Cc : 1 cc
Phenotypes:
→ CC = curly
→ Cc = curly
→ cc = straight
So 3 curly : 1 straight

✔ Genotypes: CC, Cc, cc
✔ Phenotypes: curly hair, straight hair

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Problem 9: Purebred red flower x purebred white flower (red dominant)

Red = R (dominant), white = r (recessive)
Purebred red = RR
Purebred white = rr

Cross: RR x rr

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

Genotype: all Rr
Phenotype: all red (since R is dominant)

✔ Genotypes: Rr
✔ Phenotypes: red

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Problem 10: Heterozygous tall pea plant x homozygous short pea plant

Tall = T (dominant), short = t (recessive)
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, Tt, tt, tt → 2 Tt : 2 tt → 1:1
Phenotypes:
→ Tt = tall
→ tt = short
So half tall, half short

✔ Genotypes: Tt, tt
✔ Phenotypes: tall, short

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Problem 11: Parents worried about baby with blonde hair

Mother: homozygous brown hair → let’s say B = brown (dominant), b = blonde (recessive)
So mother = BB? Wait — no! If she’s homozygous for brown, but father is heterozygous with brown hair... and some family members have blonde hair...

Wait — if blonde is recessive, then to have a blonde child (bb), BOTH parents must carry at least one b allele.

But mother is said to be “homozygous for her brown hair” → that means BB → she can ONLY give B allele.

Father is heterozygous → Bb → he can give B or b.

Possible children:
From mom: always B
From dad: B or b
→ Children: BB or Bb → ALL should have brown hair!

But baby has blonde hair → which requires bb → impossible if mom is BB.

So yes — hospital likely made a mistake.

Unless… wait — maybe “homozygous for brown hair” was misstated? But according to problem, mom is homozygous brown → BB → cannot produce blonde child.

✔ Final conclusion: Yes, hospital probably made a mistake — because two brown-haired parents where one is homozygous (BB) cannot have a blonde (bb) child.

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Final Answer:

Here are the answers for each section:

Left Worksheet:

1. Circle: A, E
2. Circle: B, C, D
3. PP, Pp
4. yy
5. TT → tall; Tt → tall; tt → short
6. Genotypes: Gg, gg → Phenotypes: grey fur, black fur
7. Genotypes: GG, Gg, gg → Phenotypes: grey fur, black fur

Right Worksheet:

8. Genotypes: CC, Cc, cc → Phenotypes: curly hair, straight hair
9. Genotypes: Rr → Phenotypes: red
10. Genotypes: Tt, tt → Phenotypes: tall, short
11. Yes, the hospital likely made a mistake — because a homozygous brown-haired mother (BB) and heterozygous brown-haired father (Bb) cannot produce a blonde-haired (bb) child. All their children should have brown hair.