Non-Mendelian Genetics Practice Problems | Assignments Genetics ... - Free Printable

Problem 1: Incomplete Dominance (Blahblah Birds)

#### Background:
- The color of blahblah birds is determined by two alleles.
- A cross between a blue bird and a white bird produces silver offspring.
- This indicates incomplete dominance, where the heterozygote (silver) has an intermediate phenotype.

#### Step-by-Step Solution:

##### a. What are the genotypes of the parent blahblah birds in the original cross?

1. Let's assign symbols to the alleles:
- Blue allele: \( B \)
- White allele: \( b \)

2. According to incomplete dominance:
- Homozygous dominant (\( BB \)): Blue
- Heterozygous (\( Bb \)): Silver (intermediate phenotype)
- Homozygous recessive (\( bb \)): White

3. The parents are:
- One parent is blue (\( BB \))
- The other parent is white (\( bb \))

Thus, the genotypes of the parent birds are:
- Blue bird: \( BB \)
- White bird: \( bb \)

##### b. What is/are the genotype(s) of the silver offspring?

1. Perform a Punnett square for the cross \( BB \times bb \):

| | \( b \) | \( b \) |
|-----|---------|---------|
| \( B \) | \( Bb \) | \( Bb \) |
| \( B \) | \( Bb \) | \( Bb \) |

2. All offspring have the genotype \( Bb \), which corresponds to the silver phenotype.

Thus, the genotype of the silver offspring is:
- \( Bb \)

##### c. What would be the phenotypic ratios of offspring produced by two silver blahblah birds?

1. The genotypes of the silver birds are \( Bb \).

2. Perform a Punnett square for the cross \( Bb \times Bb \):

| | \( B \) | \( b \) |
|-----|---------|---------|
| \( B \) | \( BB \) | \( Bb \) |
| \( b \) | \( Bb \) | \( bb \) |

3. Interpret the results:
- \( BB \): Blue (homozygous dominant)
- \( Bb \): Silver (heterozygous)
- \( bb \): White (homozygous recessive)

4. Count the phenotypes:
- Blue: 1 (\( BB \))
- Silver: 2 (\( Bb \))
- White: 1 (\( bb \))

5. Phenotypic ratio:
- Blue: \( \frac{1}{4} \) or 25%
- Silver: \( \frac{2}{4} \) or 50%
- White: \( \frac{1}{4} \) or 25%

Thus, the phenotypic ratios are:
- 25% Blue
- 50% Silver
- 25% White

---

Problem 2: Codominance (Cows)

#### Background:
- Red and white hair color in cows exhibit codominance.
- A roan cow has both red and white hairs, so its genotype is \( Rw \).
- When a roan cow (\( Rw \)) is crossed with a white cow (\( ww \)), we need to determine the genotypic and phenotypic ratios of the offspring.

#### Step-by-Step Solution:

##### a. If a roan colored cow is crossed with a white cow, what genotypic ratios are possible for the offspring?

1. Assign symbols to the alleles:
- Red allele: \( R \)
- White allele: \( w \)

2. The genotypes are:
- Roan cow: \( Rw \)
- White cow: \( ww \)

3. Perform a Punnett square for the cross \( Rw \times ww \):

| | \( w \) | \( w \) |
|-----|---------|---------|
| \( R \) | \( Rw \) | \( Rw \) |
| \( w \) | \( ww \) | \( ww \) |

4. Interpret the results:
- \( Rw \): Roan (codominant, shows both red and white)
- \( ww \): White (homozygous recessive)

5. Genotypic ratio:
- \( Rw \): 2
- \( ww \): 2

6. Convert to percentages:
- \( Rw \): \( \frac{2}{4} \) or 50%
- \( ww \): \( \frac{2}{4} \) or 50%

Thus, the genotypic ratios are:
- 50% Rw
- 50% ww

##### b. For the same cross, what phenotypes are possible for the offspring?

1. From the Punnett square:
- \( Rw \): Roan (shows both red and white)
- \( ww \): White

2. Phenotypic ratio:
- Roan: 2
- White: 2

3. Convert to percentages:
- Roan: \( \frac{2}{4} \) or 50%
- White: \( \frac{2}{4} \) or 50%

Thus, the phenotypic ratios are:
- 50% Roan
- 50% White

---

Final Answers:

#### Problem 1:
a. Genotypes of parent birds:
- Blue bird: \( BB \)
- White bird: \( bb \)

b. Genotype of silver offspring:
- \( Bb \)

c. Phenotypic ratios of offspring from two silver birds:
- 25% Blue
- 50% Silver
- 25% White

#### Problem 2:
a. Genotypic ratios of offspring from \( Rw \times ww \):
- 50% Rw
- 50% ww

b. Phenotypic ratios of offspring from \( Rw \times ww \):
- 50% Roan
- 50% White

Final Answer:
\[
\boxed{
\text{Problem 1: a) } BB \text{ and } bb, \text{ b) } Bb, \text{ c) } 25\% \text{ Blue, } 50\% \text{ Silver, } 25\% \text{ White}
}
\]
\[
\boxed{
\text{Problem 2: a) } 50\% Rw, 50\% ww, \text{ b) } 50\% \text{ Roan, } 50\% \text{ White}
}
\]