FRUIT FLY GENETICS SIMULATION
OVERVIEW: Fruit flies – the genetic whipping boy. The tiny little Drosophila melanogaster has been providing
geneticists with over a century of good times! Flies are also a pain to work with, especially if you are new at it.
With that said, we will use the benefits of the modern age and perform our fly lab squarely within the boundaries
of cyberspace. Ready? Let’s do it!
BACKGROUND: Fruit flies can reproduce an entire generation in only 2 weeks and can lay as many as 500 eggs in
10 days. The fly cultures occupy little space because the fruit flies are small; yet, they are large enough to easily
examine their genetics characteristics using a dissecting microscope. A variety of spontaneous mutations have
been found in fruit flies and other mutations have been introduced with radiation. Fruit flies have 4 pairs of
chromosomes with a tremendous number of genes to study. In this activity, you will examine only a few of the
many genes on the 4 pairs of fly chromosomes.
A fruit fly with red eyes and other normal characteristics is called a wild type. Either a wild type fly or a single wild
type gene is designated by a +. A standard name and abbreviation are designated for each mutation. The
abbreviation of a recessive gene appears only in lower case letters, while the name and abbreviation of the
dominant gene begin with a capital letter. Be aware that this simulation uses capital letters for all genes.
DIRECTIONS:
1) Go to the following website: http://www.sciencecourseware.org/vcise/drosophila/
2) Click the “Enter as a Guest” option
3) You are now in the virtual lab. Please note one very important thing – DO NOT BACK OUT OF THIS
PAGE UNTIL YOU ARE COMPLETELY DONE!!! If you back out of the page, you will have to start over.
4) The first order of business – you will need to order your fruit flies (Drosophila). Click on the
computer and use the “Order Flies” icon. We are going to perform four different crosses (but you
should only order flies for one cross at a time). For each cross, you will need to order the correct
flies:
o Cross 1: female wild type for wings X male apterous for wings
o Cross 2: female wild type for body color and wing size X male with ebony body and vestigial
wings
o Cross 3: Female wild type for eyes and wings X male with brown eyes and vestigial wings
o Cross 4: female with white eyes X male wild type for eyes
5) After ordering your flies, you will have to work through the lab until you eventually have sorted your
F1 offspring. Follow all directions on the screen in the lime-green boxes to complete each cross.
Make sure you record all of the necessary data in your F1 data table.
6) After you have recorded data for your F1 offspring, you will need to establish a cross between
members of your F1 generation. To do this, click on the piles of sorted flies to zoom in. Then click
the “Use in New Mating” button. Do this for both a male and a female. Return to your lab. Click on
the mating jar.
7) Sort your progeny/offspring and record the necessary data in the F 2 data table.
8) After you collect the F2 data, clean out your incubator by clicking on the small trash can next to it.
This resets your lab for the next cross..
9) Congratulations. The only thing left to do is the three other crosses. To order new flies, simply click
on the computer and repeat.
10) When you have completed all the crosses, you may move on to the analysis section of the lab.
DATA:
A.
One Factor (Monohybrid) Cross – Wing Size
1) In fruit flies, wild type wing size is dominant to the absence of wings (apterous). Show the cross between a wild
type female and an apterous male. What are the genotypic and phenotypic ratios of the F1 and F2 generations?
(wild type = ap+; apterous = ap)
Do the cross on paper first (below) to determine the outcome. THIS IS YOUR EXPECTED RATIO OR HYPOTHESIS.
This trait is not sex-linked, so you will not need to use X or Y.
Cross: Show your work and label the answers as F1 or F2.
2) Do the cross above using the on-line simulation. Record your data in Table 1 and Table 2 below.
Table 1: Phenotypes of the F1 Generation
Phenotype
Number of Males
Number of Females
Number of Males
Number of Females
Table 2: Phenotypes of the F2 Generation
Phenotype
DATA:
B.
Two Factor (Dihybrid) Cross of Unlinked Genes (Body Color & Wing Size)
1) In fruit flies, wild type body color (e+) is dominant to ebony (e) and wild type wing size (vg+) is dominant to
vestigial (crumpled) wings (vg). Cross a female that is wild type for both traits with a male that has an ebony body
and vestigial wings. What are the phenotypic and genotypic ratios of the F1 and F2 generations?
Do the cross on paper first to determine the outcome. THIS IS YOUR EXPECTED RATIO OR HYPOTHESIS. This is not
sex-linked so you do not have to use X or Y.
Cross: Show your work and label the answers as F1 or F2.
2) Do the cross above using the on-line simulation. Record your data in Table 1 and Table 2 below.
Table 1: Phenotypes of the F1 Generation
Phenotype
Number of Males
Number of Females
Number of Males
Number of Females
Table 2: Phenotypes of the F2 Generation
Phenotype
DATA:
C.
Cross 3: Two Factor Cross of Linked Genes (eye color and wing size)
1) In fruit flies, wild type eye are dominant to brown and wild type wings are dominant to vestigial (crumpled)
wings. Cross a female that is wild type for both traits with a male that has brown eyes and vestigial wings. What
are the phenotypic ratios of the F1? (wild type eyes = b+; brown eyes = b; wild type wings = vg+; vestigial wings = vg)
Do the cross on paper first to determine the outcome. THIS IS YOUR EXPECTED RATIO OR HYPOTHESIS.
Cross: Show your work and label the answers as F1 .
2) Now, so a testcross with an F1 offspring (female). Cross the F1 female with a male that is recessive for both traits
(brown eyes and vestigial wings). What is the phenotypic ratio of the F 2?
Cross: Show your work and label the answers are F2.
Table 1: Phenotypes of the F1 Generation
Phenotype
Number of Males
Number of Females
Number of Males
Number of Females
Table 2: Phenotypes of the F2 Generation
Phenotype
DATA:
D.
Sex-Linked Cross (eye color)
1) In fruit flies, white eye color is a sex-linked trait. Cross a white-eyed female with a wild type male. What are the
genotypic and phenotypic ratios of the F1 and F2? (Xw+ = wild type; Xw = white eyes; Y = male)
Do the cross on paper first to determine the outcome. THIS IS YOUR EXPECTED RATIO OR HYPOTHESIS.
Cross: Show your work and label the answers as F1 or F2.
2) Do the cross above using the on-line simulation. Record your data in Table 1 and Table 2 below.
Table 1: Phenotypes of the F1 Generation
Phenotype
Number of Males
Number of Females
Number of Males
Number of Females
Table 2: Phenotypes of the F2 Generation
Phenotype
ANALYSIS: Using a Chi-Square test, determine whether or not the variation between the observed and expected
number of individuals of each phenotype can adequately be explained by chance alone. Use the following formula
and determine the Chi Square value.
Next, determine the degrees of freedom. The number of degrees of freedom is always one less than the number
of phenotypes expressed in the problem.
Now, turn to the probability table below. Compare your Chi Square value with those in the row that correspond to
your degree of freedom. After determining the position of the number most nearly matching your value, look at
the head of the column it is in. The number at the head of the column is the probability (P) that the results
obtained in the experiment differ from the expected results by chance. Biologists generally reject the hypothesis if
the value of P is less than 0.05.
Probability Table:
A. One Factor (Monohybrid) Cross – Wing Size
Mode of Inheritance: __________________________________
Phenotype
Observed
Expected
X2 Value: ________________
Degrees of Freedom: ______________
Confidence Level for Hypothesis: ________________
Accepted or rejected? Explain.
Difference (o-e)
(o-e)2/Expected
B. Two Factor (Dihybrid) Cross of Unlinked Genes (Body Color & Wing Size)
Mode of Inheritance: __________________________________
Phenotype
Observed
Expected
X2 Value: ________________
Degrees of Freedom: ______________
Confidence Level for Hypothesis: ________________
Accepted or rejected? Explain.
Difference (o-e)
(o-e)2/Expected
C.
Cross 3: Two Factor Cross of Linked Genes (eye color and wing size)
Mode of Inheritance: __________________________________
Phenotype
Observed
Expected
X2 Value: ________________
Degrees of Freedom: ______________
Confidence Level for Hypothesis: ________________
Accepted or rejected? Explain.
Difference (o-e)
(o-e)2/Expected
D. Cross 4: Sex-Linked Cross (eye color)
Mode of Inheritance: __________________________________
Phenotype
Observed
Expected
X2 Value: ________________
Degrees of Freedom: ______________
Confidence Level for Hypothesis: ________________
Accepted or rejected? Explain.
Difference (o-e)
(o-e)2/Expected