Solved Genetic Crosses Worksheet Monohybrid Crosses: 1. A | Chegg.com - Free Printable

Let's solve each of these monohybrid cross problems step by step, using principles of Mendelian genetics.

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1. A heterozygous rabbit is crossed with a homozygous dominant rabbit. What are the results? (B = gray, b = white)

- Heterozygous rabbit: Bb (gray)
- Homozygous dominant rabbit: BB (gray)

Punnett Square:

| | B | B |
|-------|-------|-------|
| B | BB | BB |
| b | Bb | Bb |

Offspring Genotypes:
- 50% BB
- 50% Bb

Phenotypes:
- All offspring are gray (since B is dominant over b)

✔ Answer:
- Genotypes: 50% BB, 50% Bb
- Phenotypes: 100% gray

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2. In cats, having hair (H) is dominant over not having hair (h). A male cat that is heterozygous for hair is crossed with a hairless cat. What are the genotypes and phenotypes of their offspring?

- Male cat (heterozygous): Hh (has hair)
- Hairless cat: hh (no hair)

Punnett Square:

| | h | h |
|-------|-------|-------|
| H | Hh | Hh |
| h | hh | hh |

Offspring Genotypes:
- 50% Hh
- 50% hh

Phenotypes:
- 50% have hair (Hh)
- 50% hairless (hh)

✔ Answer:
- Genotypes: 50% Hh, 50% hh
- Phenotypes: 50% with hair, 50% hairless

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3. A homozygous dominant tomato plant is crossed with a homozygous recessive tomato plant. What are the results? (T = tall, t = short)

- Homozygous dominant: TT (tall)
- Homozygous recessive: tt (short)

Punnett Square:

| | t | t |
|-------|-------|-------|
| T | Tt | Tt |
| T | Tt | Tt |

All offspring: Tt

Genotypes: 100% Tt
Phenotypes: 100% tall (since T is dominant)

✔ Answer:
- Genotypes: All Tt
- Phenotypes: All tall

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4. If two black mice are crossed, ten black and three white mice result.

#### a. Which allele is dominant?

- Black mice produce both black and white offspring, so black must be dominant.
- White mice appear only when both alleles are recessive.

✔ Answer: Black allele is dominant.

#### b. Which allele is recessive?

- Since white mice appear in the offspring but parents are black, white must be recessive.

✔ Answer: White allele is recessive.

#### c. What are the genotypes of the parents?

- Both parents are black → could be BB or Bb
- But they produced white offspring (bb) → both parents must carry the recessive allele (b)
- So both parents must be heterozygous: Bb

✔ Answer: Both parents are Bb

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5. If long floppy ears (L) are dominant over short spiked ears (l), and you find a puppy with long floppy ears, how could you determine the puppy’s genotype?

The puppy has long floppy ears, which means it could be:
- LL (homozygous dominant) or
- Ll (heterozygous)

To determine its genotype, perform a test cross:

> Test Cross: Cross the unknown genotype (L?) puppy with a homozygous recessive individual (ll – short spiked ears).

Expected Results:

- If all offspring have long floppy ears, then the puppy is LL (no recessive alleles passed on).
- If some offspring have short spiked ears, then the puppy is Ll (passed on recessive allele).

✔ Answer:
Perform a test cross with a dog that has short spiked ears (ll).
- If all offspring have long floppy ears → puppy is LL
- If some offspring have short spiked ears → puppy is Ll

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✔ Summary of Answers:

1. Rabbits: Genotypes: 50% BB, 50% Bb; Phenotypes: 100% gray
2. Cats: Genotypes: 50% Hh, 50% hh; Phenotypes: 50% with hair, 50% hairless
3. Tomato plants: Genotypes: 100% Tt; Phenotypes: 100% tall
4. a. Black is dominant
b. White is recessive
c. Parents: both Bb
5. Perform a test cross with a short-spiked-eared dog (ll). Observe offspring to determine if the puppy is LL or Ll.

Let me know if you'd like diagrams or Punnett squares drawn out!