AP Biology: Unit 3: Cell Division & Genetics: Virtual Lab #5: Sex-Linked Traits
Instructions:
1. Open the Virtual Lab entitled “Sex-Linked Traits”:
http://www.mhhe.com/biosci/genbio/virtual_labs_2K8/labs/BL_06/index.html
2. The virtual lab simulation will be on the right side of the page, in the laboratory scene. The left
side of the page contains background information and instructions in the “Questions” area.
3. Read the background information found under the “Questions” area first, and then continue on to
reading the procedure information posted there as well.
4. When you are ready, please click on the monitor in the laboratory scene on the right side of the
page. Watch and listen to the information in the video presented to you. Next, click the
“Information” button on the bottom of the laboratory scene page and read the additional
background information on sex-linked traits.
5. Next, please click on the laboratory notebook visible in the laboratory scene. This will allow you
to practice analyzing a cross for a sex-linked trait. To begin, click on the arrow below the male
fruit fly and then on the arrow below the female fruit fly to select and establish their genotypes
on the Punnett square. You can then drag your selection from the fruit fly choices below the
Punnett square to complete the analysis of the potential offspring. When you are through, click
“Check” to evaluate your answers. If you are correct, click “Return” to go back to the laboratory
scene and begin the lab exercise. Please note that you can repeat the Punnett square exercise by
clicking “Reset” and selecting different parental genotypes if you wish.
6. Record possible genotypes in your notebook.
Female, red eyes
Female, red eyes
Female, white eyes
Male, red eyes
Male, white eyes
7. Complete the exercise as directed, recording any data or information needed in your “Data
Table” in your notebook. Make sure you mate all possible combinations in the P generation.
Table I:
Cross
Type
Phenotype
of Male
Parent
Phenotype
of Female
Parent
Number
of Red
eye, Male
Offspring
Number
of White
eye, Male
Offspring
Number
of Red
eye,
Female
Offspring
Number
of White
eye,
Female
Offspring
P
Generation
Cross
F1
Generation
Cross
P
Generation
Cross
F1
Generation
Cross
P
Generation
Cross
F1
Generation
Cross
P
Generation
Cross
F1
Generation
Cross
8. Answer the following questions in your notebook.
a. Through fruit fly studies, geneticists have discovered a segment of DNA called the
homeobox which appears to control:
i. Sex development in the flies
ii. Life span in the flies
iii. Final body plan development in the flies
b. The genotype of a red-eyed male fruit fly would be:
i. XRXR
ii. XRXr
iii. XrXr
iv. i or ii
v. None of the above
c. Sex-linked traits:
i. Can be carried on the Y chromosome
ii. Affect males and females equally
iii. Can be carried on chromosome 20
iv. i and ii
v. None of the above
d. A monohybrid cross analyzes:
i. One trait, such as eye color
ii. Two traits, such as eye color and wing shape
iii. The offspring of one parent
e. A female with the genotype “XRXr”:
i. Is homozygous for the eye color gene
ii. Is heterozygous for the eye color gene
iii. Is considered a carrier for the eye color gene
iv. i and ii
v. ii and iii
f. In T.H. Morgan’s experiments:
i. He concluded that the gene for fruit fly eye color is carried on the X chromosome.
ii. He found that his F1 generation results always mirrored those predicted by
Mendelian Laws of Inheritance.
iii. He found that his F2 generation results always mirrored those predicted by
Mendelian Laws of Inheritance.
iv. i and ii only
v. i, ii, and iii
g. In this laboratory exercise:
i. The Punnett square will allow you to predict the traits of the offspring created in
your crosses.
ii. XR will represent the recessive allele for eye color, which is white.
iii. Xr will represent the dominant allele for eye color, which is red.
iv. All of the above
h. In a cross between a homozygous red-eyed female fruit fly and a white-eyed male, what
percentage of the female offspring is expected to be carriers?
i. 0%
ii. 25%
iii. 50%
iv. 75%
v. 100%
i. In a cross between a white-eyed female and a red-eyed male:
i. All males will have red eyes.
ii. 50% of males will have white eyes.
iii. All females will have red eyes.
iv. 50% of females will have white eyes.
j. In human diseases that are X-linked dominant, one dominant allele causes the disease. If
an affected father has a child with an unaffected mother:
i. All males are unaffected.
ii. Some but not all males are affected.
iii. All females are unaffected.
iv. Some but not all females are affected.
k. In a mating between a red-eyed male fruit fly and a red-eyed heterozygous female, what
percentage of the female offspring is expected to be carriers? How did you determine the
percentage?
l. In a mating between a red-eyed male fruit fly and a white-eyed female fruit fly, what
percentage of the male offspring will have white eyes? Describe how you determined the
percentage.
m. Hemophilia, a blood disorder in humans, results from a sex-linked recessive allele.
Suppose that a daughter of a mother without the allele and a father with the allele marries
a man with hemophilia. What is the probability that the daughter's children will develop
the disease? Describe how you determined the probability.
n. Colorblindness results from a sex-linked recessive allele. Determine the genotypes of the
offspring that result from a cross between a color-blind male and a homozygous female
who has normal vision. Describe how you determined the genotypes of the offspring.
o. Explain why sex-linked traits appear more often in males than in females.
p. In humans, hemophilia is a sex-linked recessive trait. It is located on the X chromosome.
Remember that the human female genotype is XX and the male genotype is XY.
Suppose that a daughter of a mother without the allele and a father with the allele marries
a man with hemophilia. What is the probability that the daughter's children will develop
the disease? Describe how you determined the probability.
q. Colorblindness also results from a sex-linked recessive allele on the X chromosome in
humans. Determine the genotypes of the offspring that result from a cross between a
color-blind male and a homozygous female who has normal vision. Describe how you
determined the genotypes of the offspring.