Linked Traits
Virtual Lab: Sex-Linked Traits
Worksheet
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
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.
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”.
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”.
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.
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:
Through fruit fly studies, geneticists have discovered a segment of DNA called the homeobox which appears to control:
Sex development in the flies
Life span in the flies
Final body plan development in the flies
The genotype of a red-eyed male fruit fly would be:
XRXR
XRXr
XrXr
A or B
None of the above
Sex-linked traits:
Can be carried on the Y chromosome
Affect males and females equally
Can be carried on chromosome 20
A and B
None of the above -2
A monohybrid cross analyzes:
One trait, such as eye color
Two traits, such as eye color and wing shape
The offspring of one parent
A female with the genotype “XRXr”:
Is homozygous for the eye color gene
Is heterozygous for the eye color gene
Is considered a carrier for the eye color gene
A and B
B and C
In T.H. Morgan’s experiments:
He concluded that the gene for fruit fly eye color is carried on the X chromosome
He found that his F1 generation results always mirrored those predicted by Mendelian Laws of Inheritance
He found that his F2 generation results always mirrored those predicted by Mendelian Laws of Inheritance
A and B
All of the above
In this laboratory exercise:
The Punnett square will allow you to predict the traits of the offspring created in your crosses
XR will represent the recessive allele for eye color, which is white
Xr will represent the dominant allele for eye color, which is red
All of the above
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?
0%
25%
50%
75%
100%
In a cross between a white-eyed female and a red-eyed male:
All males will have red eyes
50% of males will have white eyes
All females will have red eyes
50% of females will have white eyes
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:
All males are unaffected
Some but not all males are affected
All females are unaffected
Some but not all females are affected
Journal Questions:
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