Sex linked traits -1 worksheet - Free Printable

Problem Analysis

The problem deals with sex-linked traits in fruit flies, specifically focusing on eye color. The gene for eye color is located on the X chromosome, and red eye color is dominant over white eye color. We are tasked with determining the phenotypes of offspring from specific crosses and analyzing the genotypes provided.

#### Key Points:
1. Dominance: Red eye color (R) is dominant over white eye color (r).
2. Sex chromosomes:
- Females have two X chromosomes: XX.
- Males have one X and one Y chromosome: XY.
3. Genotypes:
- Heterozygous female: \( X^R X^r \)
- Homozygous dominant female: \( X^R X^R \)
- Homozygous recessive female: \( X^r X^r \)
- Dominant male: \( X^R Y \)
- Recessive male: \( X^r Y \)

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Part 1: Determine the Sexes and Eye Colors of Flies with Given Genotypes

#### Genotypes Provided:
1. \( X^R X^r \)
2. \( X^R Y \)
3. \( X^r X^r \)
4. \( X^R X^R \)

#### Analysis:
- \( X^R X^r \): Female, heterozygous for red eyes. Phenotype: Red-eyed female.
- \( X^R Y \): Male, hemizygous for red eyes. Phenotype: Red-eyed male.
- \( X^r X^r \): Female, homozygous recessive for white eyes. Phenotype: White-eyed female.
- \( X^R X^R \): Female, homozygous dominant for red eyes. Phenotype: Red-eyed female.

#### Summary:
| Genotype | Sex | Phenotype |
|----------------|---------|-------------------|
| \( X^R X^r \) | Female | Red-eyed |
| \( X^R Y \) | Male | Red-eyed |
| \( X^r X^r \) | Female | White-eyed |
| \( X^R X^R \) | Female | Red-eyed |

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Part 2: Cross a Heterozygous Red-Eyed Female with a Red-Eyed Male

#### Parental Genotypes:
- Female: \( X^R X^r \) (heterozygous red-eyed)
- Male: \( X^R Y \) (dominant red-eyed)

#### Punnett Square:
We set up the Punnett square to determine the genotypes and phenotypes of the offspring.

| | \( X^R \) | \( X^r \) |
|-------|-----------|-----------|
| \( X^R \) | \( X^R X^R \) | \( X^R X^r \) |
| \( Y \) | \( X^R Y \) | \( X^r Y \) |

#### Offspring Genotypes and Phenotypes:
1. \( X^R X^R \): Female, homozygous dominant for red eyes. Phenotype: Red-eyed female.
2. \( X^R X^r \): Female, heterozygous for red eyes. Phenotype: Red-eyed female.
3. \( X^R Y \): Male, hemizygous for red eyes. Phenotype: Red-eyed male.
4. \( X^r Y \): Male, hemizygous for white eyes. Phenotype: White-eyed male.

#### Phenotype Percentages:
- Female Red-eyed: \( \frac{2}{4} = 50\% \)
- Female White-eyed: \( 0\% \)
- Male Red-eyed: \( \frac{1}{4} = 25\% \)
- Male White-eyed: \( \frac{1}{4} = 25\% \)

#### Summary:
| Phenotype | Percentage |
|---------------------|------------|
| Female Red-eyed | 50% |
| Female White-eyed | 0% |
| Male Red-eyed | 25% |
| Male White-eyed | 25% |

---

Part 3: Cross a White-Eyed Female with a Red-Eyed Male

#### Parental Genotypes:
- Female: \( X^r X^r \) (homozygous recessive white-eyed)
- Male: \( X^R Y \) (dominant red-eyed)

#### Punnett Square:
We set up the Punnett square to determine the genotypes and phenotypes of the offspring.

| | \( X^r \) | \( X^r \) |
|-------|-----------|-----------|
| \( X^R \) | \( X^R X^r \) | \( X^R X^r \) |
| \( Y \) | \( X^r Y \) | \( X^r Y \) |

#### Offspring Genotypes and Phenotypes:
1. \( X^R X^r \): Female, heterozygous for red eyes. Phenotype: Red-eyed female.
2. \( X^R X^r \): Female, heterozygous for red eyes. Phenotype: Red-eyed female.
3. \( X^r Y \): Male, hemizygous for white eyes. Phenotype: White-eyed male.
4. \( X^r Y \): Male, hemizygous for white eyes. Phenotype: White-eyed male.

#### Phenotype Percentages:
- Female Red-eyed: \( \frac{2}{4} = 50\% \)
- Female White-eyed: \( 0\% \)
- Male Red-eyed: \( 0\% \)
- Male White-eyed: \( \frac{2}{4} = 50\% \)

#### Summary:
| Phenotype | Percentage |
|---------------------|------------|
| Female Red-eyed | 50% |
| Female White-eyed | 0% |
| Male Red-eyed | 0% |
| Male White-eyed | 50% |

---

Final Answers:

1. Sexes and Eye Colors of Flies with Given Genotypes:
- \( X^R X^r \): Red-eyed female
- \( X^R Y \): Red-eyed male
- \( X^r X^r \): White-eyed female
- \( X^R X^R \): Red-eyed female

2. Cross Heterozygous Red-Eyed Female with Red-Eyed Male:
- Female Red-eyed: 50%
- Female White-eyed: 0%
- Male Red-eyed: 25%
- Male White-eyed: 25%

3. Cross White-Eyed Female with Red-Eyed Male:
- Female Red-eyed: 50%
- Female White-eyed: 0%
- Male Red-eyed: 0%
- Male White-eyed: 50%

$$
\boxed{
\begin{array}{l}
\text{1. } \text{Red-eyed female, Red-eyed male, White-eyed female, Red-eyed female} \\
\text{2. } \text{Female Red-eyed: 50%, Female White-eyed: 0%, Male Red-eyed: 25%, Male White-eyed: 25%} \\
\text{3. } \text{Female Red-eyed: 50%, Female White-eyed: 0%, Male Red-eyed: 0%, Male White-eyed: 50%}
\end{array}
}
$$