Free Punnett Square Practice Worksheet Collection - Free Printable

Let's go through the Punnett Square Practice Worksheet step by step and solve each part with clear explanations.

---

Part A: Vocabulary – Match the definitions on the left with the terms on the right.

We are given definitions and a list of terms (A–E). Let’s match them correctly.

1. genotypes made of the same alleles
→ This means both alleles are identical (e.g., AA or aa) → D. homozygous

2. different forms of genes for a single trait
→ These are alternative versions of a gene (e.g., A and a) → A. alleles

3. gene that is always expressed
→ This describes a dominant allele, which masks the recessive one → B. dominant

4. gene that is expressed only in the homozygous state
→ Recessive traits are only visible when no dominant allele is present → E. recessive

5. genotypes made of two different alleles
→ One dominant and one recessive (e.g., Aa) → C. heterozygous

✔ Answers:
1. D
2. A
3. B
4. E
5. C

---

Circle the choices that are examples of each of those words.

#### 6. Homozygous dominant
→ Two identical dominant alleles (capital letters):
- AA ✔
- KK ✔
- TT ✔

So circle: AA, KK, TT

#### 7. Homozygous recessive
→ Two identical recessive alleles (lowercase letters):
- ee ✔
- qq ✔
- ww ✔

So circle: ee, qq, ww

#### 8. Genotypes in which dominant gene must show
→ Dominant traits are expressed in homozygous dominant (AA) and heterozygous (Aa) genotypes. So any genotype with at least one capital letter will show the dominant trait.

Look at the options:
- AA ✔ (shows dominant)
- Dd ✔ (shows dominant)
- EE ✔ (shows dominant)
- ff ✘ (no dominant, recessive)
- Jj ✔ (shows dominant)
- RR ✔ (shows dominant)
- Ss ✔ (shows dominant)

So circle: AA, Dd, EE, Jj, RR, Ss

> Note: "ff" does not show dominant — it shows recessive.

#### 9. Genotypes in which recessive gene must show
→ Recessive traits are only expressed when both alleles are recessive (homozygous recessive).

So only:
- aa ✔
- rr ✔
- ff ✔

Wait — look at the list:
- aa ✔
- Gg ✘ (heterozygous, dominant shown)
- Ff ✘
- KK ✘
- rr ✔
- Oo ✘
- Tt ✘

Only aa and rr are homozygous recessive.

But wait — what about ff? It’s also homozygous recessive. But it's not listed here.

Given: aa, Gg, Ff, KK, rr, Oo, Tt

So only aa and rr are homozygous recessive.

✔ Circle: aa, rr

> Note: Ff has an f, but since it’s paired with F (dominant), the trait is not expressed. Only aa and rr will express recessive traits.

---

Part B: Punnett Squares

#### 10. Examine the following Punnett squares and circle those that are correct.

Let’s evaluate each:

(1)
```
D d
d Dd dd
d Dd dd
```

- Parent 1: Dd
- Parent 2: dd
- Offspring: Dd, dd, Dd, dd → Correct ratio: 2 Dd : 2 dd → ✔️ Correct

(2)
```
D D
d Dd DD
d Dd Dd
```

- Parent 1: DD
- Parent 2: dd
- Offspring: Dd, DD, Dd, Dd → Wait! That gives DD, which can't happen from DD × dd. Should be all Dd.

This is wrong. The top row should be D and D, bottom row d and d → so offspring: Dd, Dd, Dd, Dd → All Dd.

But this square shows DD, which is impossible.

✘ Incorrect

(3)
```
A a
A AA aa
a Aa Aa
```

Parent 1: Aa
Parent 2: Aa
Offspring: AA, aa, Aa, Aa → This is wrong.

Correct offspring from Aa × Aa:
- AA, Aa, Aa, aa → But in this square, AA and aa are both in the same box — but they should be in separate boxes.

Actually, the square shows:
- Top-left: AA → OK
- Top-right: aa → ✘ Wrong! Should be Aa
- Bottom-left: Aa → OK
- Bottom-right: Aa → OK

But top-right is aa, which is incorrect. Should be Aa.

✘ Incorrect

(4)
```
A a
a Aa aa
a Aa aa
```

Parent 1: Aa
Parent 2: aa
Offspring: Aa, aa, Aa, aa → That’s correct.

✔️ Correct

✔ So correct Punnett squares are (1) and (4) → Circle these.

---

#### 11. What do the letters on the outside of the Punnett square stand for?

→ They represent the alleles contributed by each parent (gametes). Each parent contributes one allele per gene.

✔ Answer: The letters on the outside represent the gametes (sex cells) of each parent.

---

#### 12. What do the letters on the inside of the Punnett square stand for?

→ They represent the genotypes of the possible offspring.

✔ Answer: The letters inside represent the possible genotypes of the offspring.

---

#### 13. In corn plants, normal height, N, is dominant to short height, n.

We need to complete four Punnett squares for different crosses, then:

- Circle homozygous dominant (NN)
- Put an X through heterozygous (Nn)
- Leave homozygous recessive (nn) unshaded

Let’s go one by one.

---

Cross 1: NN × nn

```
N N
n Nn Nn
n Nn Nn
```

All offspring: Nn → Heterozygous

- No NN → nothing circled
- All Nn → put X through all four boxes
- No nn → none unshaded

Final:
```
N N
n X X
n X X
```

---

Cross 2: Nn × Nn

```
N n
N NN Nn
n Nn nn
```

Offspring:
- Top-left: NN → circle (homozygous dominant)
- Top-right: Nn → X (heterozygous)
- Bottom-left: Nn → X
- Bottom-right: nn → leave unshaded (homozygous recessive)

Final:
```
N n
N ○ X
n X (leave blank)
```

---

Cross 3: Nn × nn

```
N n
N NN Nn
n Nn nn
```

Wait — actually, parent 1 is Nn, parent 2 is nn → gametes: N, n and n, n

So:
```
N n
n Nn nn
n Nn nn
```

Offspring:
- Nn → X (heterozygous)
- nn → unshaded
- Nn → X
- nn → unshaded

No NN → nothing circled

Final:
```
N n
n X (blank)
n X (blank)
```

---

Cross 4: nn × nn

```
n n
n nn nn
n nn nn
```

All offspring: nn → homozygous recessive → all unshaded

No circles, no X’s.

Final:
```
n n
n (blank) (blank)
n (blank) (blank)
```

---

✔ Final Answers Summary

---

Part A: Matching

1. D (homozygous)
2. A (alleles)
3. B (dominant)
4. E (recessive)
5. C (heterozygous)

---

Part A: Circle Examples

6. Homozygous dominant: AA, KK, TT
7. Homozygous recessive: ee, qq, ww
8. Genotypes where dominant gene must show: AA, Dd, EE, Jj, RR, Ss
9. Genotypes where recessive gene must show: aa, rr

---

Part B: Punnett Squares

10. Correct ones: First and fourth (the ones with Dd/dd and Aa/aa crosses) → Circle those two

11. Outside letters: Gametes (parental alleles)
12. Inside letters: Offspring genotypes

13. Completed Punnett squares:

#### Cross 1: NN × nn
```
N N
n X X
n X X
```

#### Cross 2: Nn × Nn
```
N n
N ○ X
n X (blank)
```

#### Cross 3: Nn × nn
```
N n
n X (blank)
n X (blank)
```

#### Cross 4: nn × nn
```
n n
n (blank) (blank)
n (blank) (blank)
```

---

Let me know if you'd like this as a printable version or need help drawing it out!