Virtual Lab: Sex-Linked Traits

Virtual Lab:  Sex-Linked Traits

Worksheet

 

 

  1. Please make sure you have read through all of the information in the “Questions” and “Information” areas. If you come upon terms that are unfamiliar to you, please refer to your textbook for further explanation or search the word here:  http://encarta.msn.com/encnet/features/dictionary/dictionaryhome.aspx
  2. Next, complete the Punnett square activity by clicking on the laboratory notebook. Please be sure to note the possible genotypes of the various flies:
Female, red eyes Female, red eyes Female, white eyes Male, red eyes Male, white eyes
XRXR XrXR XrXr XRY XrY

 

 

When you have completed the Punnett square activity, return to the laboratory scene to begin the actual laboratory activity.

  1. In this exercise, you will perform a Drosophila mating in order to observe sex-linked trait transmission. Please click on the shelf in the laboratory.  Here you will find vials of fruit flies.  On the TOP shelf, please click on one of the female vials (on the left side) and then drag it to the empty vial on the shelf below.  Please repeat this step using one of the male vials (on the right side).  These flies will be used as the parental (P) generation. You may switch your parent choices at any time by dragging out old selections and dragging in new flies. Use the Punnett square below to predict the genotypes/phenotypes of the offspring (Note:  refer to the genotype table you created above if needed):
  XR XR
XR Genotype: XRXR

Phenotype:Red eye, female

Genotype:XRXR

Phenotype: Red eye, female

Y Genotype:XRY

Phenotype: Red eye, male

Genotype:XRY

Phenotype: Red eye, male

 

__50_% Female, red eye    _0__% Female, white eye      _50__% Male, red eye   _0__% Male, white eye

 

When you are finished, click “Mate and Sort”.

  1. You will now see information appear in the vials sitting on the next shelf below. These are the offspring of the parent flies you selected above, and they represent the first filial (F1) generation.  In your “Data Table” on the bottom of the page and/or on Table I found at the end of this Worksheet, please input the numbers of each sex and phenotype combination for the F1 generation.  These numbers will be placed into the first row marked “P generation Cross”.
  2. You will next need to select one of the F1 female flies and one of the F1 male flies to create the second filial (F2) generation. Drag your selections down to the empty vial on the next shelf below and fill in the Punnett square below to predict the offspring:

 

  XR XR
XR Genotype: XRXR

Phenotype:Red eye, female

Genotype:XRXR

Phenotype: Red eye, female

Y Genotype:XRY

Phenotype: Red eye, male

Genotype:XRY

Phenotype: Red eye, male

 

 

 

__50_% Female, red eye    _0__% Female, white eye      _50__% Male, red eye   _0__% Male, white eye

 

After clicking “Mate and Sort”, you will now have information on their offspring (the F2 generation) to input into your “Data Table” or Worksheet below.  This information will be placed into the second row marked “F1 generation Cross”.

NOTE:  there are additional lines remaining to use if your instructor requires the analysis of additional crosses.

  1. Please finish this exercise by opening the “Journal” link at the bottom of the page and answering the questions.

 

 

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 Red Red 50 0 50 0
F1 Generation Cross Red Red 50 0 50 0
P Generation Cross White Red 47 0 53 0
F1 Generation Cross Red Red 22 25 53 0
P Generation Cross Red White 0 49 51 0
F1 Generation Cross White Red 27 28 20 25
P Generation Cross White White 0 51 0 49
F1 Generation Cross White White 0 51 0 49

 

 

 

 

 

 

Post-laboratory Questions:

 

  1. Through fruit fly studies, geneticists have discovered a segment of DNA called the homeobox which appears to control:
  2. Sex development in the flies
  3. Life span in the flies
  4. Final body plan development in the flies

 

  1. The genotype of a red-eyed male fruit fly would be:
  2. XRXR
  3. XRXr
  4. XrXr
  5. A or B
  6. None of the above

 

  1. Sex-linked traits:
  2. Can be carried on the Y chromosome
  3. Affect males and females equally
  4. Can be carried on chromosome 20
  5. A and B
  6. None of the above -2

 

  1. A monohybrid cross analyzes:
  2. One trait, such as eye color
  3. Two traits, such as eye color and wing shape
  4. The offspring of one parent

 

  1. A female with the genotype “XRXr”:
  2. Is homozygous for the eye color gene
  3. Is heterozygous for the eye color gene
  4. Is considered a carrier for the eye color gene
  5. A and B
  6. B and C

 

  1. In T.H. Morgan’s experiments:
  2. He concluded that the gene for fruit fly eye color is carried on the X chromosome
  3. He found that his F1 generation results always mirrored those predicted by Mendelian Laws of Inheritance
  4. He found that his F2 generation results always mirrored those predicted by Mendelian Laws of Inheritance
  5. A and B
  6. All of the above

 

  1. In this laboratory exercise:
  2. The Punnett square will allow you to predict the traits of the offspring created in your crosses
  3. XR will represent the recessive allele for eye color, which is white
  4. Xr will represent the dominant allele for eye color, which is red
  5. All of the above

 

  1. 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?
  2. 0%
  3. 25%
  4. 50%
  5. 75%
  6. 100%

 

  1. In a cross between a white-eyed female and a red-eyed male:
  2. All males will have red eyes
  3. 50% of males will have white eyes
  4. All females will have red eyes
  5. 50% of females will have white eyes

 

  1. 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:

 

  1. All males are unaffected
  2. Some but not all males are affected
  3. All females are unaffected
  4. Some but not all females are affected

 

Journal Questions:

 

  1. 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?

 

  1. 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.

 

  1. 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.

 

 

  1. 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.

 

  1. Explain why sex-linked traits appear more often in males than in females.

 

  1. 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.

 

  1. 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.

 

  1. Based on the traits explained in questions 6 and 7, explain why sex-linked traits in humans appear more often in males than in females.

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