Objective: Students will learn and apply the principles of Mendelian inheritance by experimentation with the fruit fly Drosophila melanogaster. Students will make hypotheses for monohybrid, dihybrid and sex-linked traits and test their hypotheses by selecting fruit flies with different visible mutations, mating them, and analyzing the phenotypic ratios of the offspring. Students will record their observations into an online notebook and write a lab report.
**Teachers will need to set this account up before students can proceed with the registration and assignments **
Website: http://www.sciencecourseware.org/vcise/ --- Click on the Drosophila Link
1. Create a new account
2. Class code (see your instructor)
3. Enter your first and last name (your username will be generated for you)
4. Choose a password ' Write down your user name and passwords!
Notebook: The top tab contains a "notebook" link where you can enter data gathered during your experiments. Also in the notebook tab, you will write your report. All notebook data and report data will be saved and sent to your teacher upon completion.
Understanding the Program
1. Start by ordering two wild type
flies and mate them.
2. View your flies under the microscope and sort them.
3. View the flies close-up and note the difference between males and females.
4. Add your data to your notebook.
5. Use the computer to "analyze results"
6. Go to the chi square analysis. Enter your hypothesis. Since both of your parents with wild type, you would expect a 50:50 ratio of male to females. You will need to you a calculator to determine the expected numbers from the total number of offspring you have. Enter that number in the "hypothesis" column.
7. The computer will do the chi square analysis for you and show your statistical results.
8. Return to your notebook and look at your data.
9. "Save" your notebook.
**Just play with the simulator for now to see what it does. Remove all your data from your notebook before you start the real assignments.
1. Choose ONE trait
from the autosomal mutations on the table to study by ordering flies of
the mutant strain and crossing it with a wild type fly.
2. Cross your flies (P generation) and determine the phenotype of the F1 generation.
3. Now mate the offspring (F1) from that cross together (creates F2 generation). Return to the lab and choose "use fly in new mating" under the microscope view.
4. Sort your F2 flies and analyze results. You can choose to ignore sex here, since you know you are studying only autosomal mutations. Show that your results follow a 3:1 ratio.
5. Run a chi square analysis on your F2 flies (again you can ignore sex).
1. A reciprocal cross is a wild type male x mutant female followed by a mutant male x wild type female. (Obviously, you study the same trait here). Choose an allele found on the sex chromosome. [See chromosome map for sex linked alleles]
2. Show in your notebook how the
offspring differ depending on which parent had the mutant phenotype. Be prepared
to explain why this happens in your final lab report. You only need to look
at the F1 generation here.
1. Select any two traits on two different
chromosomes and study their inheritance patterns
(DIHYBRID CROSS) [See chromosome map] . Also be sure that you do not pick any traits that are LETHAL as this will skew your data.
(a) Cross an F1 offspring with another
F1 offspring to generate an F2 generation. This should demonstrate a 9:3:3:1
(b) Test the 9:3:3:1 ratio by using a chi-square analysis.
(a) Select two traits on the same
chromosome and study their inheritance patterns (excludes sex-linked and lethal
mutations). [See chromosome map].
(b) Cross a double mutant with a wild type. Choose traits that are less than 20 map units apart.
(c) What do you EXPECT from this cross? What are the observed outcomes? What are the genotypes and phenotypes of your F1 generation? What are the genotypes and phenotypes of your F2 generation? Do you observe any crossing over (based on your outcomes?)
(d) Determine what happens when you
choose traits that are much farther apart by crossing a new set of flies. Your
results will vary due to the frequency of crossing-over. Be able to explain
these varied results on your lab report. Use the F1 and F2 generation to determine
how expected outcomes differ when distant alleles are involved
(a) Choose a lethal allele and mate
two flies that both have this allele.
(b) What are the phenotypes of the offspring and in what proportion? How does this differ from non-lethal alleles?
(c) What is dominant (mutant or wild-type)? How can you tell from the cross?