Punnett Square Practice Problems - Free Printable

Problem Analysis and Solutions

The document contains several genetics problems involving Punnett squares, dominant and recessive traits, and probability calculations. Below is a detailed explanation and solution for each problem.

---

#### 1. Seals (Whisker Length)
Problem:
Let's say in seals, the gene for the length of the whiskers has two alleles. The dominant allele (V) codes for long whiskers, and the recessive allele (v) codes for short whiskers.
- Question 1: What percentage of offspring would be expected to have short whiskers if one parent is homozygous dominant (VV) and the other is heterozygous (Vv)?

Solution:
- Genotypes of Parents:
- Parent 1: Homozygous dominant = VV
- Parent 2: Heterozygous = Vv

- Punnett Square:
```
V v
V VV Vv
V VV Vv
```

- Offspring Genotypes:
- All offspring will have either VV or Vv.
- Since V is dominant over v, all offspring will have long whiskers.

- Percentage of Short Whiskers:
- No offspring will have short whiskers because all will have at least one V allele.
- Answer: 0%

---

#### 2. Seals (Whisker Length)
Problem:
If one parent seal is pure long-whiskered (homozygous dominant, VV) and the other is short-whiskered (homozygous recessive, vv), what percent of offspring would have short whiskers?

Solution:
- Genotypes of Parents:
- Parent 1: Homozygous dominant = VV
- Parent 2: Homozygous recessive = vv

- Punnett Square:
```
V v
V Vv Vv
```

- Offspring Genotypes:
- All offspring will have the genotype Vv.
- Since V is dominant over v, all offspring will have long whiskers.

- Percentage of Short Whiskers:
- No offspring will have short whiskers because all will have at least one V allele.
- Answer: 0%

---

#### 3. Purple People Eaters (Horns)
Problem:
In purple people eaters, one-horn is dominant and no horn is recessive. Draw a Punnett square showing the cross of a purple people eater that is hybrid for horns (Aa) with a purple people eater that does not have horns (aa).

Solution:
- Genotypes of Parents:
- Parent 1: Hybrid for horns = Aa
- Parent 2: No horns = aa

- Punnett Square:
```
A a
a Aa aa
a Aa aa
```

- Offspring Genotypes & Phenotypes:
- Aa: One-horn (dominant phenotype)
- aa: No horns (recessive phenotype)

- Summary:
- 50% Aa (one-horn)
- 50% aa (no horns)

Answer:
- Punnett Square:
```
A a
a Aa aa
a Aa aa
```
- Summary:
- 50% one-horn (Aa)
- 50% no horns (aa)

---

#### 4. Fuzzywhatsits (Leaf Color)
Problem:
A green-leafed fuzzywhatsit (JJ) is crossed with a fuzzywhatsit with yellow-striped leaves (jj). The cross produces 185 green-leafed fuzzywhatsits. Summarize the genotypes and phenotypes of the possible offspring.

Solution:
- Genotypes of Parents:
- Parent 1: Green-leafed (homozygous dominant) = JJ
- Parent 2: Yellow-striped (homozygous recessive) = jj

- Punnett Square:
```
J j
J JJ Jj
J JJ Jj
```

- Offspring Genotypes & Phenotypes:
- JJ: Green-leafed (dominant phenotype)
- Jj: Green-leafed (dominant phenotype)

- Summary:
- All offspring will have the genotype JJ or Jj, both of which result in green leaves.
- Answer:
- 100% green-leafed (JJ or Jj)

---

#### 5. Fuzzywhatsits (Leaf Color)
Problem:
What were the genotypes of both parents if the cross produces 185 green-leafed fuzzywhatsits?

Solution:
- From the previous problem, we know that the cross between JJ (green-leafed) and jj (yellow-striped) results in all green-leafed offspring (JJ or Jj).
- Answer:
- Parent 1: JJ (green-leafed)
- Parent 2: jj (yellow-striped)

---

#### 6. Fuzzywhatsits (Leaf Color)
Problem:
Summarize the genotypes and phenotypes of the offspring that would be produced by crossing two of the green-leafed fuzzywhatsits obtained from the initial cross.

Solution:
- From the previous cross (JJ × jj), the offspring are all Jj (hybrid green-leafed).
- Now, we cross two hybrids (Jj × Jj):
- Punnett Square:
```
J j
J JJ Jj
j Jj jj
```

- Offspring Genotypes & Phenotypes:
- JJ: Green-leafed (dominant phenotype)
- Jj: Green-leafed (dominant phenotype)
- jj: Yellow-striped (recessive phenotype)

- Summary:
- 75% green-leafed (JJ or Jj)
- 25% yellow-striped (jj)

Answer:
- Punnett Square:
```
J j
J JJ Jj
j Jj jj
```
- Summary:
- 75% green-leafed (JJ or Jj)
- 25% yellow-striped (jj)

---

#### 7. Wrinkle-Seeded Plants
Problem:
Mendel found that crossing wrinkled-seeded plants with pure round-seeded plants produced only round-seeded plants. What genotypic and phenotypic ratios can be expected from a cross of a wrinkled-seeded plant (rr) and a plant heterozygous for this trait (Rr)?

Solution:
- Genotypes of Parents:
- Parent 1: Wrinkled-seeded (homozygous recessive) = rr
- Parent 2: Heterozygous round-seeded = Rr

- Punnett Square:
```
r r
R Rr Rr
r rr rr
```

- Offspring Genotypes & Phenotypes:
- Rr: Round-seeded (dominant phenotype)
- rr: Wrinkled-seeded (recessive phenotype)

- Summary:
- 50% Rr (round-seeded)
- 50% rr (wrinkled-seeded)

Answer:
- Punnett Square:
```
r r
R Rr Rr
r rr rr
```
- Summary:
- 50% round-seeded (Rr)
- 50% wrinkled-seeded (rr)

---

#### 8. Deafness in Dogs
Problem:
In dogs, there is a hereditary deafness caused by a recessive gene, "d." A kennel owner has a male dog that she wants to use for breeding purposes if possible. The dog can hear, so the owner knows his genotype is either DD or Dd. If the dog’s genotype is Dd, the owner does not wish to use him for breeding because the deafness gene will not be passed on. This can be tested by breeding the dog to a deaf female (dd). Draw the Punnett squares to illustrate these two possible crosses. In each case, what percentage/how many of the offspring would be expected to be hearing? Deaf?

Solution:
- Case 1: Male Dog is DD (Hearing)
- Genotypes of Parents:
- Male: DD
- Female: dd
- Punnett Square:
```
D D
d Dd Dd
d Dd Dd
```
- Offspring Genotypes & Phenotypes:
- Dd: Hearing (dominant phenotype)
- Summary:
- 100% hearing (Dd)

- Case 2: Male Dog is Dd (Hearing)
- Genotypes of Parents:
- Male: Dd
- Female: dd
- Punnett Square:
```
D d
d Dd dd
d Dd dd
```
- Offspring Genotypes & Phenotypes:
- Dd: Hearing (dominant phenotype)
- dd: Deaf (recessive phenotype)
- Summary:
- 50% hearing (Dd)
- 50% deaf (dd)

Answer:
- Case 1 (DD × dd):
- Punnett Square:
```
D D
d Dd Dd
d Dd Dd
```
- Summary:
- 100% hearing (Dd)

- Case 2 (Dd × dd):
- Punnett Square:
```
D d
d Dd dd
d Dd dd
```
- Summary:
- 50% hearing (Dd)
- 50% deaf (dd)

---

#### 9. Determining the Genotype of the Male Dog
Problem:
How could you tell the genotype of this male dog?

Solution:
- Breed the male dog with a deaf female (dd).
- If all offspring are hearing, the male dog is homozygous dominant (DD).
- If some offspring are deaf, the male dog is heterozygous (Dd).

Answer:
- Breed the male dog with a deaf female (dd). Observe the offspring:
- If all offspring are hearing, the male dog is DD.
- If some offspring are deaf, the male dog is Dd.

---

#### 10. Deaf Offspring from Hearing Dogs
Problem:
Using Punnett square(s), show how two hearing dogs could produce deaf offspring.

Solution:
- Both hearing dogs must be heterozygous (Dd).
- Genotypes of Parents:
- Parent 1: Dd
- Parent 2: Dd

- Punnett Square:
```
D d
D DD Dd
d Dd dd
```

- Offspring Genotypes & Phenotypes:
- DD: Hearing (dominant phenotype)
- Dd: Hearing (dominant phenotype)
- dd: Deaf (recessive phenotype)

- Summary:
- 75% hearing (DD or Dd)
- 25% deaf (dd)

Answer:
- Punnett Square:
```
D d
D DD Dd
d Dd dd
```
- Summary:
- 75% hearing (DD or Dd)
- 25% deaf (dd)

---

Final Answers:

1. 0%
2. 0%
3.
- Punnett Square:
```
A a
a Aa aa
a Aa aa
```
- Summary:
- 50% one-horn (Aa)
- 50% no horns (aa)
4.
- Punnett Square:
```
J j
J JJ Jj
J JJ Jj
```
- Summary:
- 100% green-leafed (JJ or Jj)
5.
- Parent 1: JJ
- Parent 2: jj
6.
- Punnett Square:
```
J j
J JJ Jj
j Jj jj
```
- Summary:
- 75% green-leafed (JJ or Jj)
- 25% yellow-striped (jj)
7.
- Punnett Square:
```
r r
R Rr Rr
r rr rr
```
- Summary:
- 50% round-seeded (Rr)
- 50% wrinkled-seeded (rr)
8.
- Case 1 (DD × dd):
- Punnett Square:
```
D D
d Dd Dd
d Dd Dd
```
- Summary:
- 100% hearing (Dd)
- Case 2 (Dd × dd):
- Punnett Square:
```
D d
d Dd dd
d Dd dd
```
- Summary:
- 50% hearing (Dd)
- 50% deaf (dd)
9.
- Breed the male dog with a deaf female (dd). Observe the offspring:
- If all offspring are hearing, the male dog is DD.
- If some offspring are deaf, the male dog is Dd.
10.
- Punnett Square:
```
D d
D DD Dd
d Dd dd
```
- Summary:
- 75% hearing (DD or Dd)
- 25% deaf (dd)

Final Answer Boxed:
\boxed{0\%, 0\%, \text{See explanations}, \text{See explanations}, \text{See explanations}, \text{See explanations}, \text{See explanations}, \text{See explanations}, \text{See explanations}, \text{See explanations}}