Genetics practice worksheet featuring Punnett squares to determine probabilities of offspring genotypes for traits like brown vs. blue eyes, curly vs. straight hair, and freckles.

Let's solve each Punnett square step by step and determine the probabilities for each genotype and phenotype.

---

1. Brown eyes (B) are dominant over blue eyes (b)

Cross: Bb × bb

#### Punnett Square:
```
B b
-------------
b | Bb | bb
-------------
b | Bb | bb
```

#### Genotype Probabilities:
- BB = 0% → Not possible
- Bb = 2 out of 4 = 50%
- bb = 2 out of 4 = 50%

✔ Answer:
- BB: 0%
- Bb: 50%
- bb: 50%

---

2. Curly hair (C) is dominant over straight hair (c)

Cross: CC × Cc

#### Punnett Square:
```
C C
-------------
C | CC | CC
-------------
c | Cc | Cc
```

#### Genotype Probabilities:
- CC = 2 out of 4 = 50%
- Cc = 2 out of 4 = 50%
- cc = 0% → Not possible

✔ Answer:
- CC: 50%
- Cc: 50%
- cc: 0%

---

3. Freckles (F) are dominant over no freckles (f)

#### a. Homozygous recessive freckles × Homozygous dominant freckles

- Homozygous recessive freckles = ff
- Homozygous dominant freckles = FF

Cross: ff × FF

#### Punnett Square:
```
F F
-------------
f | Ff | Ff
-------------
f | Ff | Ff
```

All offspring = Ff

#### Phenotype Probabilities:
- Freckles (Ff) = 100% → Since F is dominant
- No freckles = 0%

✔ Answer:
- Freckles: 100%
- No freckles: 0%

---

#### b. Heterozygous freckles × Homozygous dominant freckles

- Heterozygous freckles = Ff
- Homozygous dominant freckles = FF

Cross: Ff × FF

#### Punnett Square:
```
F F
-------------
F | FF | FF
-------------
f | Ff | Ff
```

Offspring: FF (50%), Ff (50%)

All have at least one F → all have freckles

#### Phenotype Probabilities:
- Freckles = 100%
- No freckles = 0%

✔ Answer:
- Freckles: 100%
- No freckles: 0%

---

#### c. Heterozygous freckles × Heterozygous freckles

- Both parents = Ff

Cross: Ff × Ff

#### Punnett Square:
```
F f
-------------
F | FF | Ff
-------------
f | Ff | ff
```

Offspring:
- FF = 1/4 = 25%
- Ff = 2/4 = 50%
- ff = 1/4 = 25%

Phenotypes:
- Freckles (FF or Ff) = 75%
- No freckles (ff) = 25%

✔ Answer:
- Freckles: 75%
- No freckles: 25%

---

#### d. Heterozygous freckles × Homozygous recessive freckles

- Heterozygous freckles = Ff
- Homozygous recessive freckles = ff

Cross: Ff × ff

#### Punnett Square:
```
f f
-------------
F | Ff | Ff
-------------
f | ff | ff
```

Offspring:
- Ff = 2/4 = 50%
- ff = 2/4 = 50%

Phenotypes:
- Freckles (Ff) = 50%
- No freckles (ff) = 50%

✔ Answer:
- Freckles: 50%
- No freckles: 50%

---

✔ Final Answers Summary:

---

1. Bb × bb (Eye color):
- BB: 0%
- Bb: 50%
- bb: 50%

2. CC × Cc (Hair type):
- CC: 50%
- Cc: 50%
- cc: 0%

---

3. Freckles (F dominant):

a. ff × FF
- Freckles: 100%
- No freckles: 0%

b. Ff × FF
- Freckles: 100%
- No freckles: 0%

c. Ff × Ff
- Freckles: 75%
- No freckles: 25%

d. Ff × ff
- Freckles: 50%
- No freckles: 50%

---

📌 Key Concepts:

- Dominant alleles (B, C, F) mask recessive ones.
- Homozygous = same alleles (BB, bb, FF, ff)
- Heterozygous = different alleles (Bb, Cc, Ff)
- Punnett squares predict genotype and phenotype ratios in offspring.

Let me know if you'd like a visual version or help with labeling the squares!