Genetics Worksheets and Printables - Free Printable

Worksheet Analysis and Solution

The worksheet focuses on sex-linked inheritance in fruit flies, specifically using the example of eye color as a sex-linked trait. Below is a detailed explanation and solution for each section.

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#### Section 1: Match the correct definitions

We need to match the terms on the left with their correct definitions on the right.

| Term (Left) | Definition (Right) |
|-------------|--------------------|
| B 1. Non-sex chromosomes. | B. Autosomes |
| D 2. Genes that reside on X chromosomes. | F. X-linked dominant inheritance |
| E 3. Genes that reside on the Y chromosome. | E. Y-linked |
| J 4. Common example of a Y-linked disorder. | J. Jacobs syndrome |
| H 5. An inheritance pattern in which a trait is inherited by the second generation via a carrier from the first generation. Also known as skip generation inheritance. | G. X-linked recessive inheritance |
| K 6. An individual who carries a gene mutation and is able to pass the gene mutation on to the next generation. | K. Carrier |
| A 7. Type of chromosome that is involved in sex determination. | A. Sex chromosomes |
| C 8. Genes that are found on sex chromosomes. | C. Sex-linked |
| I 9. Common example of an X-linked condition. | I. Color blindness |
| F 10. Mode of inheritance in which a dominant gene is carried on an X chromosome. | F. X-linked dominant inheritance |
| G 11. Mode of inheritance in which recessive mutations are found on the X chromosome(s). | G. X-linked recessive inheritance |

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#### Section 2: Monohybrid cross problems

##### Problem 12: Identify the sex and eye colors of the following genotypes

Given:
- Red eye color (R) is dominant.
- White eye color (r) is recessive.

We analyze each genotype:

1. a. \( X^R X^R \)
- Sex: Female (two X chromosomes)
- Eye color: Red (homozygous dominant)

2. b. \( X^r Y \)
- Sex: Male (one X and one Y chromosome)
- Eye color: White (recessive allele on X chromosome)

3. c. \( X^R Y \)
- Sex: Male (one X and one Y chromosome)
- Eye color: Red (dominant allele on X chromosome)

4. d. \( X^r X^r \)
- Sex: Female (two X chromosomes)
- Eye color: White (homozygous recessive)

5. e. \( X^R X^r \)
- Sex: Female (two X chromosomes)
- Eye color: Red (heterozygous, dominant allele expresses)

6. f. \( X^r X^r \)
- Sex: Female (two X chromosomes)
- Eye color: White (homozygous recessive)

Answers:
- a. Female, red
- b. Male, white
- c. Male, red
- d. Female, white
- e. Female, red
- f. Female, white

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##### Problem 13: Determine the possible genotypes of the following fly phenotypes

1. a. Male, red eyes
- Male flies have one X chromosome and one Y chromosome.
- Since red eyes are dominant (\( R \)), the genotype must include at least one \( R \) allele.
- Possible genotype: \( X^R Y \)

2. b. Female, red eyes
- Female flies have two X chromosomes.
- Since red eyes are dominant (\( R \)), the genotype can be either homozygous dominant or heterozygous.
- Possible genotypes: \( X^R X^R \) or \( X^R X^r \)

3. c. Female, white eyes
- Female flies have two X chromosomes.
- Since white eyes are recessive (\( r \)), both X chromosomes must carry the recessive allele.
- Possible genotype: \( X^r X^r \)

4. d. Male, white eyes
- Male flies have one X chromosome and one Y chromosome.
- Since white eyes are recessive (\( r \)), the X chromosome must carry the recessive allele.
- Possible genotype: \( X^r Y \)

Answers:
- a. \( X^R Y \)
- b. \( X^R X^R \) or \( X^R X^r \)
- c. \( X^r X^r \)
- d. \( X^r Y \)

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##### Problem 14: Cross between a male fruit fly with white eyes and a female fruit fly heterozygous for red eyes

1. a. What are the genotypes of the parents?
- Male fruit fly with white eyes: \( X^r Y \)
- Female fruit fly heterozygous for red eyes: \( X^R X^r \)

2. b. Prepare a monohybrid cross.
- Parental genotypes:
- Male: \( X^r Y \)
- Female: \( X^R X^r \)
- Punnett square:
```
| X^R | X^r |
---------------------
Y | X^R Y | X^r Y |
---------------------
X^r | X^R X^r | X^r X^r |
```

3. c. What are the possible genotypes of the offspring?
- From the Punnett square:
- \( X^R Y \)
- \( X^r Y \)
- \( X^R X^r \)
- \( X^r X^r \)

4. d. What are the possible phenotypes of the offspring?
- Male offspring:
- \( X^R Y \): Red eyes
- \( X^r Y \): White eyes
- Female offspring:
- \( X^R X^r \): Red eyes (heterozygous)
- \( X^r X^r \): White eyes

Phenotypes:
- Male, white eyes
- Male, red eyes
- Female, red eyes
- Female, white eyes

Final Answers:
- a. Genotypes of parents: \( X^r Y \) (male), \( X^R X^r \) (female)
- b. Monohybrid cross (Punnett square shown above)
- c. Possible genotypes of offspring: \( X^R Y \), \( X^r Y \), \( X^R X^r \), \( X^r X^r \)
- d. Possible phenotypes of offspring: Male, white eyes; Male, red eyes; Female, red eyes; Female, white eyes

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Final Answer Box:

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\text{See detailed solutions above.}
}
\]