Using FlyLab JS
Go to the Flylab JS website:
GENETICS LAB #3:
In this week’s lab, you will be using a virtual fly breeding simulation to deepen your
understanding of gene linkage and X-linked inheritance. Please follow the instructions below to
answer the questions at the end of the lab.
Go to the Flylab JS website:
FlyLab JS is a web-based genetics simulation program where you are provided a series of
potential genotypes of fruit flies to cross, and you can analyze the offspring of that cross to
determine the relative dominance of the traits.
To set up crosses, you select the trait you wish to
investigate (Body Color in the example on the left),
and then select a phenotype for the fly of your
choice (Yellow in this example). You can select
phenotypes for as many traits as you choose. When
you have designed your fly of interest, click on the
“Select Fly for Mating” button. You will then be
prompted to design the second fly of the mating pair.
Once you have selected this fly to mate, click on the
“Mate” button shown between the flies. The result
will be graphical depictions of every possible
offspring phenotype, as well as numerical breakdowns of how many offspring of each sex were
I strongly recommend that you set up several P0, F1, and F2 crosses of various types before
starting the assignment, to help you better understand the interface. To see how many offspring
of each phenotype you get from a cross, you can look at the numbers written above each
offspring phenotype. However, I recommend clicking on the
“Analyze” tab at the top of the screen (shown to the right). This
presents the data in tabular form, and you can have it show the
proportions of each genotype segregated by sex, or in total.
Comparing the relative ratios in this way can help make the process
The FlyLab JS website labels their genotypes differently than we cover in lecture. For any gene
that the fly exhibits a wild type phenotype, they do not label the gene at all. Flies that are
completely wild type are labeled only with a plus sign (‘+’). Any fly that shows a mutant
phenotype is labeled with the gene abbreviation in capital letters (Y, W, CY, AP). Note: Flylab
indicates the phenotype of each fly, but does not display the genotype.
Your Assignment –
You will be setting up several fly crosses, comparing offspring ratios, and determining the mode
of inheritance of those genes. We will be using mutants in the white gene and in the miniature
gene for this lab. The white gene and the miniature gene are both located on the X chromosome.
Follow the instructions below, and answer all questions.
Select a female fly with the White Eye Color trait, and mate her to a male fly with the Miniature
Wing Size trait.
Q1. What are the phenotypes of the offspring from this cross?
Q2. How many of each phenotype are there? You may find it helpful to answer this
question by selecting the “Analyze” tab, and checking the box labeled “Ignore sex of flies,” as
shown in the image on the previous page.
Select the female offspring of cross #1, and mate her to a male fly showing both the White Eye
Color trait and the Miniature Wing Size trait.
Q3. What are the phenotypes of the offspring from this cross?
Q4. How many of each phenotype are there?
Q5. Assume these genes are inherited through simple Mendelian inheritance. Set up a
Punnett’s Square of cross #2. Do the Punnett’s Square results match the results you observe?
Explain why or why not.
Q6. Write the genotypes of each of the parents and offspring in crosses #1 and #2.
Remember, these genes are on the X chromosome.
Q7. Are the mutant alleles in the female parent in cross #2 in cis or in trans? Draw a
diagram of the arrangement of her alleles on both of her X chromosomes.
Q8. For each gene, which alleles are dominant and negative?
Q9. Consider your answer to Q8. What is the name for the specific type of cross you set
up for cross #2?
Q11. Propose a non-Mendelian mode of inheritance for the white and miniature genes.
Q12. How far apart on the X chromosome are the white and miniature genes? You must
show all work to receive any credit for this question.
Repeat crosses #1 and #2 using either one of the two genes listed above and the Yellow allele of
the Body Color trait. Then answer questions #6 and #12 for these new crosses.
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