Worksheet for practicing Punnett squares, including vocabulary definitions, genotype identification, and genetic cross diagrams.

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 in corn).

3. gene that is always expressed → B. dominant
*Explanation:* Dominant alleles mask recessive ones and are expressed even if only one copy is present.

4. gene that is expressed only in the homozygous state → E. recessive
*Explanation:* Recessive alleles are only expressed when no dominant allele is present (i.e., in homozygous recessive condition like nn).

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

✔ 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
These have two identical capital letters (same dominant alleles).
- AA ✔
- Gg ✘ (heterozygous)
- KK ✔
- mm ✘ (homozygous recessive)
- uu ✘ (homozygous recessive)
- Rr ✘ (heterozygous)
- TT ✔

✔ Answer: AA, KK, TT

#### 7. Homozygous recessive
These have two identical lowercase letters (same recessive alleles).
- ee ✔
- Ff ✘
- HH ✘ (dominant)
- Oo ✘
- qq ✔
- Uu ✘
- ww ✔

✔ Answer: ee, qq, ww

#### 8. Genotypes in which dominant gene must show
Dominant traits are expressed when at least one dominant allele is present (i.e., genotype has at least one capital letter).
But the question says “must show” — so we want genotypes where the dominant trait will definitely be expressed. That means homozygous dominant (AA, EE, RR), and heterozygous (Dd, Jj, Ss) also express the dominant trait.

So all genotypes with at least one capital letter will show the dominant trait.

- AA ✔
- Dd ✔
- EE ✔
- ff ✘ (only recessive)
- Jj ✔
- RR ✔
- Ss ✔

✔ Answer: AA, Dd, EE, Jj, RR, Ss

> Note: "ff" does not show dominant trait, so it’s excluded.

#### 9. Genotypes in which recessive gene must show
Recessive traits are only expressed when there are no dominant alleles, i.e., homozygous recessive (both lowercase).

- aa ✔
- Gg ✘ (has G, so dominant shows)
- Ff ✘
- KK ✘
- rr ✔
- Oo ✘
- Tt ✘

✔ Answer: aa, rr

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Part B: Punnett Squares

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

We’ll analyze each:

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Square 1:
```
D d
d Dd dd
d Dd dd
```
- Parents: Dd × dd
- Offspring: Dd, dd, Dd, dd → 2 Dd : 2 dd → Correct.
✔ Correct

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Square 2:
```
D D
d Dd DD
d Dd Dd
```
- Parents: DD × dd
- Offspring should be all Dd.
- But here: Dd, DD, Dd, Dd → Includes DD, which is impossible from DD × dd.
✘ Incorrect

---

Square 3:
```
A a
A AA aa
a Aa Aa
```
- Parents: Aa × Aa
- Offspring should be: AA, Aa, Aa, aa → but here top-right is aa, bottom-left is Aa, etc.
Wait: Let's check:
- Top-left: A×A = AA ✔
- Top-right: A×a = Aa ✘ (but shown as aa)
- Bottom-left: a×A = Aa ✘ (shown as Aa? Wait: row is 'a', column is 'A' → Aa)
Wait: actually:
- Row labels: A, a
- Column labels: A, a
So:
- A×A = AA ✔
- A×a = Aa ✔
- a×A = Aa ✔
- a×a = aa ✔

But in the square:
- Top-left: AA ✔
- Top-right: aa ✘ (should be Aa)
- Bottom-left: Aa ✔
- Bottom-right: Aa ✘ (should be aa)

So this square is wrongly filled.

✘ Incorrect

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Square 4:
```
A a
a Aa aa
a Aa aa
```
- Parents: Aa × aa
- Offspring: Aa, aa, Aa, aa → Correct (1:1 ratio)
✔ Correct

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✔ Correct Punnett squares: Square 1 and Square 4

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

➡️ The letters on the outside represent the alleles from each parent (gametes).

Each parent contributes one allele per gene. So these are the parental gametes.

✔ Answer: The gametes (sex cells) of the parents.

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

➡️ The letters on the inside represent the genotypes of the offspring resulting from combining the parental gametes.

✔ Answer: The genotypes of the offspring.

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#### 13. In corn plants, normal height, N, is dominant to short height, n. Complete these four Punnett squares showing different crosses. Then, circle all of the homozygous dominant offspring. Put an X through all the heterozygous offspring. Leave all the homozygous recessive offspring unshaded.

Let’s complete each cross.

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Cross 1: NN × nn

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

All offspring: Nn → Heterozygous

- Circle: none (no homozygous dominant)
- Put X through: all four (all are Nn)
- Leave unshaded: none (no homozygous recessive)

✔ Final:
```
N N
n Nn Nn
n Nn Nn
```
All boxes have X (since all are heterozygous)

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Cross 2: Nn × Nn

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

Offspring:
- NN → homozygous dominant → circle
- Nn → heterozygous → X
- Nn → X
- nn → homozygous recessive → leave blank

✔ Final:
```
N n
N NN Nn
n Nn nn
```
- Circle: NN (top-left)
- X: both Nn (top-right, bottom-left)
- nn (bottom-right): leave blank

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Cross 3: Nn × nn

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

Offspring:
- Nn → heterozygous → X
- nn → homozygous recessive → blank
- Nn → X
- nn → blank

✔ Final:
```
N n
n Nn nn
n Nn nn
```
- X on both Nn
- nn boxes remain blank

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Cross 4: nn × nn

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

All offspring: nn → homozygous recessive → leave blank

✔ Final:
```
n n
n nn nn
n nn nn
```
All boxes blank (no circles, no X)

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✔ Summary of Part B - Question 13:

Completed Punnett Squares:

1. NN × nn
```
N N
n Nn Nn
n Nn Nn
```
→ All boxes marked with X

2. Nn × Nn
```
N n
N NN Nn
n Nn nn
```
→ Circle: NN
→ X: Nn (top-right, bottom-left)
→ Blank: nn (bottom-right)

3. Nn × nn
```
N n
n Nn nn
n Nn nn
```
→ X: Nn (top-left, bottom-left)
→ Blank: nn (top-right, bottom-right)

4. nn × nn
```
n n
n nn nn
n nn nn
```
→ All blank

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✔ Final Answers Recap:

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

#### 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

#### 10. Correct Punnett squares: First and Fourth
#### 11. Outside letters: Parental gametes (alleles from each parent)
#### 12. Inside letters: Offspring genotypes
#### 13. Completed Punnett squares: As above, with circles, X’s, and blanks applied accordingly.

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