Monohybrid Cross Worksheet | Slides Genetics | Docsity - Free Printable

Here's the complete solution to your Monohybrid Cross Worksheet, with clear explanations for each part.

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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 identical (e.g., NN or nn).*

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 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 traits only show up when an organism has two copies (e.g., nn).*

5. genotypes made of two different alleles → C. heterozygous
*Explanation:* Heterozygous means having two different alleles (e.g., Nn).*

✔ Answers:
1. D
2. A
3. B
4. E
5. C

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## Part B: Punnett Squares

Question 6: Corn Plants — Normal Height (N) vs. Short Height (n)

We’re told:
- N = dominant (normal height)
- n = recessive (short height)

You must complete 4 Punnett squares and shade:
- Red: homozygous dominant offspring (NN)
- Green: heterozygous offspring (Nn)
- Unshaded: homozygous recessive (nn)

Let’s fill each square:

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#### Square 1: Parents = NN × nn

| | N | N |
|-------|-------|-------|
| n | Nn | Nn |
| n | Nn | Nn |

→ All offspring = Nn → Heterozygous → Shade GREEN

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#### Square 2: Parents = Nn × NN

| | N | n |
|-------|-------|-------|
| N | NN | Nn |
| N | NN | Nn |

→ Offspring: 2 NN (homozygous dominant → RED), 2 Nn (heterozygous → GREEN)

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#### Square 3: Parents = Nn × Nn

| | N | n |
|-------|-------|-------|
| N | NN | Nn |
| n | Nn | nn |

→ Offspring: 1 NN (RED), 2 Nn (GREEN), 1 nn (unshaded)

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#### Square 4: Parents = Nn × nn

| | N | n |
|-------|-------|-------|
| n | Nn | nn |
| n | Nn | nn |

→ Offspring: 2 Nn (GREEN), 2 nn (unshaded)

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✔ Summary of Shading:

- Square 1: All 4 green
- Square 2: 2 red, 2 green
- Square 3: 1 red, 2 green, 1 unshaded
- Square 4: 2 green, 2 unshaded

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Question 7: Guinea Pigs — Short Hair (S) vs. Long Hair (s)

#### a. One guinea pig is Ss and one is ss

Parental genotypes: Ss × ss

Punnett Square:

| | S | s |
|-------|-------|-------|
| s | Ss | ss |
| s | Ss | ss |

→ Offspring: 2 Ss (short hair), 2 ss (long hair)

✔ Expected number of offspring:
- Short hair (SS or Ss) → 2 (Note: SS doesn’t appear here, but Ss does → still short hair)
- Long hair (ss) → 2

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#### b. Both guinea pigs are heterozygous for short hair → Ss × Ss

Punnett Square:

| | S | s |
|-------|-------|-------|
| S | SS | Ss |
| s | Ss | ss |

→ Offspring: 1 SS, 2 Ss, 1 ss

Phenotype:
- Short hair (SS or Ss) → 3 out of 4 → 3
- Long hair (ss) → 1 out of 4 → 1

✔ Expected number of offspring:
- Short hair → 3
- Long hair → 1

*(Note: Since it says “expected number,” and Punnett squares show ratios, we assume 4 total offspring for simplicity.)*

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## Part C: Monohybrid Cross Problems

Question 8: Hornless (H) vs. Horned (h) in Cattle

> A homozygous hornless bull (HH) is mated with a homozygous horned cow (hh).

Parents: HH × hh

Punnett Square:

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

→ All offspring = Hh

✔ Genotype of F1 generation: All Hh
✔ Phenotype of F1 generation: All hornless (since H is dominant)

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Question 9: Tongue Rolling in Humans — Roller (R) vs. Non-Roller (r)

> A man who is a non-roller marries a woman who is heterozygous for tongue rolling.

- Man (non-roller) → genotype rr (must be homozygous recessive)
- Woman (heterozygous roller) → genotype Rr

Cross: rr × Rr

Punnett Square:

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

→ Offspring: 2 Rr (rollers), 2 rr (non-rollers)

✔ Genotypic ratio: 1 Rr : 1 rr
✔ Phenotypic ratio: 1 roller : 1 non-roller

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## ✔ Final Answers Summary:

Part A:

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

Part B – Q6: (Shading as explained above)

Part B – Q7:

a. Short hair: 2, Long hair: 2
b. Short hair: 3, Long hair: 1

Part C:

Q8. Genotype: All Hh, Phenotype: All hornless
Q9. Offspring: 50% rollers (Rr), 50% non-rollers (rr)

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