Worksheet for practicing Punnett squares, including vocabulary matching and genetic crosses.

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

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

1. genotypes made of the same alleles → D. homozygous
*Explanation:* Homozygous means both alleles are the same (e.g., AA or aa).

2. different forms of genes for a single trait → A. alleles
*Explanation:* Alleles are alternative versions of a gene (e.g., N and n for height).

3. gene that is always expressed → B. dominant
*Explanation:* Dominant alleles are expressed even if only one copy is present (e.g., N in Nn).

4. gene that is expressed only in the homozygous state → E. recessive
*Explanation:* Recessive alleles are only expressed when two copies are present (e.g., nn).

5. genotypes made of two different alleles → C. heterozygous
*Explanation:* Heterozygous means one dominant and one recessive allele (e.g., Nn).

✔ Answers:
1-D, 2-A, 3-B, 4-E, 5-C

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

6. Homozygous dominant → Genotypes with two identical dominant alleles:
- AA, KK, TT
✔ Circle: AA, KK, TT

7. Homozygous recessive → Genotypes with two identical recessive alleles:
- ee, qq, ww
✔ Circle: ee, qq, ww

8. Genotypes in which dominant gene must show → These are genotypes where the dominant allele is present (either homozygous or heterozygous), so it will be expressed:
- AA, Dd, EE, RR, Ss
*(Note: ff, Jj — but Jj has J and j; unless J is dominant, we assume capital = dominant)*
So: AA, Dd, EE, RR, Ss
Also: Jj (if J is dominant) → yes, because dominant allele is present.
But ff is homozygous recessive → no dominant expression.
✔ Circle: AA, Dd, EE, Jj, RR, Ss

9. Genotypes in which recessive gene must show → Only when homozygous recessive, because recessive traits are masked in heterozygotes:
- aa, rr, oo
*(Note: Gg, Ff, KK, Tt have dominant alleles, so recessive not shown)*
✔ Circle: aa, rr, oo

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Part B: Punnett Squares

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

Let’s analyze each:

#### Square 1:
```
D d
d | Dd dd
d | Dd dd
```
- Parental gametes: D and d from top, d and d from side.
- Offspring: Dd, dd, Dd, dd → Correct.
✔ Correct

#### Square 2:
```
D D
d | Dd DD
d | Dd DD
```
- Top: D and D, Side: d and d → Gametes are D and D (from one parent), d and d (from other).
- Offspring: Dd, DD, Dd, DD → This would happen if one parent is DD and the other is dd.
- But the setup shows DD x dd → Yes, this is valid.
✔ Correct

#### Square 3:
```
A a
a | Aa aa
a | Aa aa
```
- Parents: Aa × aa → Offspring: Aa, aa, Aa, aa → Correct.
✔ Correct

#### Square 4:
```
A a
a | Aa aa
a | Aa aa
```
- Same as above? Wait, this is identical to square 3.
- Actually, it's identical to square 3. So also correct.
✔ Correct

Wait! Let's check again: Are they really the same?

No — wait, actually, the second row is a a, so it's Aa x aa → same as before.

But let's look carefully:

- Square 3:
```
A a
a | Aa aa
a | Aa aa
```

- Square 4:
```
A a
a | Aa aa
a | Aa aa
```

They are identical. So both are correct.

✔ All four are correct.
So circle all four.

But wait — let’s double-check Square 2:
- If one parent is DD, gametes: D, D
- Other parent is dd, gametes: d, d
- Offspring: Dd, Dd, Dd, Dd → All Dd?
- But here it shows: Dd, DD, Dd, DD → That’s wrong!

Ah! Mistake!

In Square 2:
```
D D
d | Dd DD
d | Dd DD
```
This implies:
- Parent 1: DD → gametes: D, D
- Parent 2: dd → gametes: d, d
- Offspring should be: Dd, Dd, Dd, Dd → All Dd
- But this square shows DD and Dd → Incorrect

✘ Square 2 is incorrect

Now check Square 1:
- Parent 1: Dd → gametes: D, d
- Parent 2: dd → gametes: d, d
- Offspring: Dd, dd, Dd, dd → Correct ✔

Square 3:
- Parent 1: Aa → gametes: A, a
- Parent 2: aa → gametes: a, a
- Offspring: Aa, aa, Aa, aa → Correct ✔

Square 4:
- Same as 3 → ✔

But Square 2 is wrong — it shows DD offspring from dd × DD cross → impossible.

So only Square 1, 3, and 4 are correct.

✔ Circle: Square 1, 3, and 4

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11. What do the letters on the outside of the Punnett square stand for?
👉 Gametes (or alleles from each parent)
Each letter represents an allele contributed by one parent.

12. What do the letters on the inside of the Punnett square stand for?
👉 Genotypes of the offspring
Each box shows the combination of alleles from both parents.

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13. Corn plants: Normal height (N) is dominant to short height (n). Complete these four Punnett squares showing different crosses. Then:

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

Let’s do each cross:

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#### Cross 1: NN × nn
```
N N
n | Nn Nn
n | Nn Nn
```
All offspring: Nn → heterozygous
→ Put X through all boxes

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#### Cross 2: Nn × Nn
```
N n
N | NN Nn
n | Nn nn
```
- NN → homozygous dominant → circle
- Nn → heterozygous → X
- Nn → X
- nn → homozygous recessive → leave blank

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#### Cross 3: NN × Nn
```
N n
N | NN Nn
N | NN Nn
```
- NN → circle
- Nn → X
- NN → circle
- Nn → X

---

#### Cross 4: nn × nn
```
n n
n | nn nn
n | nn nn
```
All offspring: nn → homozygous recessive → leave all blank

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✔ Final Answer Summary:

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Part A: Matching

1. D
2. A
3. B
4. E
5. C

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Part A: Circles

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

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Part B: Punnett Squares

10. Correct squares:
- First (Dd × dd) ✔
- Third (Aa × aa) ✔
- Fourth (same as third) ✔
✘ Second is incorrect (shows DD offspring from DD × dd → impossible)

11. Outside letters: Parental gametes (alleles)
12. Inside letters: Offspring genotypes

13. Completed Punnett Squares:

#### Cross 1: NN × nn
```
N N
n | Nn Nn
n | Nn Nn
```
→ All X (heterozygous)

#### Cross 2: Nn × Nn
```
N n
N | NN Nn
n | Nn nn
```
- Circle: NN
- X: Nn, Nn
- nn: blank

#### Cross 3: NN × Nn
```
N n
N | NN Nn
N | NN Nn
```
- Circle: NN, NN
- X: Nn, Nn

#### Cross 4: nn × nn
```
n n
n | nn nn
n | nn nn
```
→ All blank (homozygous recessive)

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✔ Worksheet complete!
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