Genetics Practice Problems worksheet for students to learn about dominant and recessive traits.

Let's go through each section of the Genetics Practice Problems worksheet step by step and solve them with explanations.

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1. For each genotype below, indicate whether it is heterozygous (He) or homozygous (Ho)

Definitions:
- Homozygous (Ho): Two identical alleles (both dominant or both recessive).
- Heterozygous (He): Two different alleles (one dominant, one recessive).

| Genotype | Answer |
|---------|--------|
| AA | Ho |
| Bb | He |
| Ce | He |
| Dd | He |
| Ee | He |
| ff | Ho |
| GG | Ho |
| HH | Ho |
| Ii | He |
| Jj | He |
| kk | Ho |
| Ll | He |
| Mm | He |
| nn | Ho |
| OO | Ho |
| Pp | He |

> ✔ Explanation:
> - Homozygous = same letters (AA, ff, GG, etc.)
> - Heterozygous = different letters (Bb, Dd, Ee, etc.)

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2. For each genotype, determine what phenotypes would be possible

We use the dominance rules given:

#### Purple flowers are dominant to white
- P = purple (dominant), p = white (recessive)

| Genotype | Phenotype |
|---------|-----------|
| PP | Purple |
| Pp | Purple |
| pp | White |

> ✔ Explanation: Since P is dominant, any P present results in purple flowers. Only pp shows white.

#### Brown eyes are dominant to blue
- B = brown (dominant), b = blue (recessive)

| Genotype | Phenotype |
|---------|-----------|
| BB | Brown |
| Bb | Brown |
| bb | Blue |

> ✔ Explanation: B is dominant → BB and Bb both show brown; only bb shows blue.

#### Round seeds are dominant to wrinkled
- R = round (dominant), r = wrinkled (recessive)

| Genotype | Phenotype |
|---------|-----------|
| RR | Round |
| Rr | Round |
| rr | Wrinkled |

> ✔ Explanation: R is dominant → RR and Rr are round; rr is wrinkled.

#### Bobtails are recessive (to long tails)
- T = long tail (dominant), t = bobtail (recessive)

| Genotype | Phenotype |
|---------|-----------|
| TT | Long tail |
| Tt | Long tail |
| tt | Bobtail |

> ✔ Explanation: T is dominant → TT and Tt have long tails; only tt has a bobtail.

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3. For each phenotype, list the genotypes

Use the letter of the dominant trait.

#### Straight hair is dominant to curly
- S = straight (dominant), s = curly (recessive)

| Phenotype | Genotype(s) |
|----------|-------------|
| straight | SS or Ss |
| straight | SS or Ss |
| curly | ss |

> ✔ Explanation: Straight can be SS or Ss (since S is dominant). Curly must be ss.

#### Tail spikes are dominant to plain tails
- S = spikes (dominant), s = plain (recessive)

| Phenotype | Genotype(s) |
|----------|-------------|
| spikes | SS or Ss |
| spikes | SS or Ss |
| plain | ss |

> ✔ Explanation: Spikes = SS or Ss; plain = ss.

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4. Set up Punnett squares for each cross. Round seeds are dominant to wrinkled.

Let:
- R = round (dominant)
- r = wrinkled (recessive)

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#### Cross 1: Rr × rr

Parent 1 (Rr) gametes: R, r
Parent 2 (rr) gametes: r, r

Punnett Square:

| | r | r |
|-------|-------|-------|
| R | Rr | Rr |
| r | rr | rr |

Offspring:
- Rr → round (2 out of 4)
- rr → wrinkled (2 out of 4)

✔ Percentage of offspring that will be round?
→ 2/4 = 50%

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#### Cross 2: Rr × Rr

Gametes: R, r from both parents

Punnett Square:

| | R | r |
|-------|-------|-------|
| R | RR | Rr |
| r | Rr | rr |

Offspring:
- RR → round
- Rr → round
- rr → wrinkled

Genotypic ratio: 1 RR : 2 Rr : 1 rr
Phenotypic ratio: 3 round : 1 wrinkled

✔ Percentage of offspring that will be round?
→ 3/4 = 75%

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#### Cross 3: RR × Rr

Parent 1 (RR) gametes: R, R
Parent 2 (Rr) gametes: R, r

Punnett Square:

| | R | r |
|-------|-------|-------|
| R | RR | Rr |
| R | RR | Rr |

Offspring:
- All have at least one R → all are round

Genotypes: 2 RR, 2 Rr → all round

✔ Percentage of offspring that will be round?
→ 4/4 = 100%

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✔ Final Answers Summary

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#### 1. Homozygous (Ho) or Heterozygous (He)?

| Genotype | Answer |
|---------|--------|
| AA | Ho |
| Bb | He |
| Ce | He |
| Dd | He |
| Ee | He |
| ff | Ho |
| GG | Ho |
| HH | Ho |
| Ii | He |
| Jj | He |
| kk | Ho |
| Ll | He |
| Mm | He |
| nn | Ho |
| OO | Ho |
| Pp | He |

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#### 2. Phenotypes

- Purple flowers:
PP → Purple
Pp → Purple
pp → White

- Brown eyes:
BB → Brown
Bb → Brown
bb → Blue

- Round seeds:
RR → Round
Rr → Round
rr → Wrinkled

- Tail length:
TT → Long tail
Tt → Long tail
tt → Bobtail

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#### 3. Genotypes from Phenotypes

- Straight hair: SS or Ss
- Curly hair: ss
- Spikes: SS or Ss
- Plain tail: ss

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#### 4. Punnett Squares & Percentages

| Cross | Percentage Round |
|--------------|------------------|
| Rr × rr | 50% |
| Rr × Rr | 75% |
| RR × Rr | 100% |

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