Dihybrid Cross Worksheet | Lecture notes Genetics | Docsity - Free Printable

Problem: Dihybrid Cross Worksheet

#### Question 1: Set up a Punnett square using the following information
- Dominant allele for tall plants = D
- Recessive allele for dwarf plants = d
- Dominant allele for purple flowers = W
- Recessive allele for white flowers = w
- Cross a homozygous dominant parent (DDWW) with a homozygous recessive parent (ddww).

#### Solution for Question 1:
To set up the Punnett square, we need to determine the gametes produced by each parent:
- The homozygous dominant parent (DDWW) will produce only one type of gamete: DW.
- The homozygous recessive parent (ddww) will produce only one type of gamete: dw.

The Punnett square will look like this:

| | DW | DW | DW | DW |
|-------|------|------|------|------|
| dw| DdWw | DdWw | DdWw | DdWw |
| dw| DdWw | DdWw | DdWw | DdWw |

All offspring will have the genotype DdWw.

#### Question 2: Using the Punnett square in question #1:
a. What is the probability of producing tall plants with purple flowers?
b. What is the probability of producing dwarf plants with white flowers?
c. What is the probability of producing tall plants with white flowers?
d. What is the probability of producing dwarf plants with purple flowers?

#### Solution for Question 2:
From the Punnett square in Question 1, all offspring have the genotype DdWw. Let's analyze each part:

a. Tall plants with purple flowers:
- Tall plants are determined by the presence of at least one D allele (heterozygous or homozygous dominant).
- Purple flowers are determined by the presence of at least one W allele (heterozygous or homozygous dominant).
- All offspring have DdWw, which means they are tall and have purple flowers.
- Probability: 100% (or 1)
- Possible genotype(s): DdWw

b. Dwarf plants with white flowers:
- Dwarf plants are determined by the homozygous recessive genotype dd.
- White flowers are determined by the homozygous recessive genotype ww.
- None of the offspring have the genotype ddww.
- Probability: 0%
- Possible genotype(s): None

c. Tall plants with white flowers:
- Tall plants are determined by the presence of at least one D allele.
- White flowers are determined by the homozygous recessive genotype ww.
- None of the offspring have the genotype D_ww.
- Probability: 0%
- Possible genotype(s): None

d. Dwarf plants with purple flowers:
- Dwarf plants are determined by the homozygous recessive genotype dd.
- Purple flowers are determined by the presence of at least one W allele.
- None of the offspring have the genotype ddW_.
- Probability: 0%
- Possible genotype(s): None

---

#### Question 3: Set up a Punnett square using the following information
- Dominant allele for black fur in guinea pigs = B
- Recessive allele for white fur in guinea pigs = b
- Dominant allele for rough fur in guinea pigs = R
- Recessive allele for smooth fur in guinea pigs = r
- Cross a heterozygous parent (BbRr) with a heterozygous parent (BbRr).

#### Solution for Question 3:
To set up the Punnett square, we need to determine the gametes produced by each parent:
- The heterozygous parent (BbRr) can produce four types of gametes: BR, Br, bR, and br.

The Punnett square will look like this:

| | BR | Br | bR | br |
|-------|------|------|------|------|
| BR| BBRR | BBRr | BbRR | BbRr |
| Br| BBRr | BBrr | BbRr | Bbrr |
| bR| BbRR | BbRr | bbRR | bbRr |
| br| BbRr | Bbrr | bbRr | bbrr |

#### Question 4: Using the Punnett square in question #3:
a. What is the probability of producing guinea pigs with black, rough fur?
b. What is the probability of producing guinea pigs with black, smooth fur?
c. What is the probability of producing guinea pigs with white, rough fur?
d. What is the probability of producing guinea pigs with white, smooth fur?

#### Solution for Question 4:
From the Punnett square in Question 3, we can count the number of offspring with each phenotype:

a. Black, rough fur:
- Black fur is determined by the presence of at least one B allele.
- Rough fur is determined by the presence of at least one R allele.
- Offspring with black, rough fur: BBRR, BBRr, BbRR, BbRr
- Total favorable outcomes: 9
- Total possible outcomes: 16
- Probability: 9/16
- Possible genotype(s): BBRR, BBRr, BbRR, BbRr

b. Black, smooth fur:
- Black fur is determined by the presence of at least one B allele.
- Smooth fur is determined by the homozygous recessive genotype rr.
- Offspring with black, smooth fur: BBrr, Bbrr
- Total favorable outcomes: 3
- Total possible outcomes: 16
- Probability: 3/16
- Possible genotype(s): BBrr, Bbrr

c. White, rough fur:
- White fur is determined by the homozygous recessive genotype bb.
- Rough fur is determined by the presence of at least one R allele.
- Offspring with white, rough fur: bbRR, bbRr
- Total favorable outcomes: 3
- Total possible outcomes: 16
- Probability: 3/16
- Possible genotype(s): bbRR, bbRr

d. White, smooth fur:
- White fur is determined by the homozygous recessive genotype bb.
- Smooth fur is determined by the homozygous recessive genotype rr.
- Offspring with white, smooth fur: bbrr
- Total favorable outcomes: 1
- Total possible outcomes: 16
- Probability: 1/16
- Possible genotype(s): bbrr

---

Final Answers:

#### Question 1:
Punnett square:
```
| | DW | DW | DW | DW |
|-------|------|------|------|------|
| dw| DdWw | DdWw | DdWw | DdWw |
| dw| DdWw | DdWw | DdWw | DdWw |
```

#### Question 2:
a. Probability: 100% (1), Genotype: DdWw
b. Probability: 0%, Genotype: None
c. Probability: 0%, Genotype: None
d. Probability: 0%, Genotype: None

#### Question 3:
Punnett square:
```
| | BR | Br | bR | br |
|-------|------|------|------|------|
| BR| BBRR | BBRr | BbRR | BbRr |
| Br| BBRr | BBrr | BbRr | Bbrr |
| bR| BbRR | BbRr | bbRR | bbRr |
| br| BbRr | Bbrr | bbRr | bbrr |
```

#### Question 4:
a. Probability: 9/16, Genotype: BBRR, BBRr, BbRR, BbRr
b. Probability: 3/16, Genotype: BBrr, Bbrr
c. Probability: 3/16, Genotype: bbRR, bbRr
d. Probability: 1/16, Genotype: bbrr

Final Answer:
\boxed{
\text{See detailed solutions above.}
}