Fruit Fly Genetics | Mutation | Drosophila Melanogaster

Name(s): Per/row: Fruit Fly Genetics Lab Lab adapted from http://www.biologycorner.com/fruitflygenetics/index.html

*All links can be found on Mrs. Davisson’s website under “AP bio lab” tab Background Information: Drosophila melanogaster is a fruit fly, a little insect about 3mm long, of the kind that accumulates around spoiled fruit. It is also one of the most valuable of organisms in biological research, particularly in genetics and developmental biology. Drosophila has been used as a model organism for research for almost a century, mainly because it is practical: it's a small animal, with a short life cycle of just two weeks, and is cheap and easy to keep large numbers. Mutant flies, with defects in any of several thousand genes are available, and the entire genome has recently been sequenced. See mutant fruit flies: http://www.exploratorium.edu/exhibits/mutant_flies/mutant_flies.html Terminology Wild-type - flies that have the "normal" characteristics, red eyes, normal length wing and brown bodies. Mutant flies - any variation from the wild type. Mutant alleles can be carried on autosomes or sex chromosomes. Genetic Notation Mutant flies are given names that generally denote the type of mutation the fly exhibits. For example, the mutant "ebony" has a much darker body than the wild type fly. Each mutation is also given a letter code. Thus, in the case of ebony, the code is a lower case e. The wild type fly can be denoted by a superscript + over the mutant letter code. For example, e+ denotes a wild type fly for the ebony body trait - meaning it has normal body color or black (not ebony). The above description is for a gene located on an autosome (a non-sex chromosome). e+e+ = wild type (or EE) *the reason for this notation is that the wild type e+e = heterozygous (or Ee) can either be dominant or recessive ee= ebony Of course, fruit flies also have sex chromosomes and they contain a subset of genes as well. The genotypic notation for a mutant gene for white eye color on the X chromosome would look like: Xw Xw = white-eyed female Xw+Xw = wild type heterozygote female Xw Y = white-eyed male Xw+ Y = wild type male If needed, review how to do chi-squared: http://www.ndsu.edu/pubweb/~mcclean/plsc431/mendel/mendel4.htm *Reminder: For genetics problems, your null hypothesis is that there will be no difference between the predicted phenotype ratio that is found with a Punnett square and the actual phenotypes seen in experimental data. If you accept the null hypothesis, this means your predicted pattern of inheritance was correct. If you reject your null hypothesis, this mean it is unlikely that this was the actual pattern of inheritance. In this case, it could mean something else is influencing the inheritance of the genes, such as sex-linked, multiple alleles, linked genes, genetic disease, environmental influence or hormonal influence. Prelab Questions: 1. Why are fruit flies a good subject for genetic studies?

A. Sexing Fruit Flies: http://www.biologycorner.com/fruitflygenetics/sex.html 1. Anesthetize and then click on the flies to see the gender. Look at their stripes. Describe the differences between male fruit flies and female fruit flies. 1

2. How many male fruit flies were present in the simulation? ______ How many females? ______ B. Cross 1: Wild Type Female x Vestigial Winged Male: http://www.biologycorner.com/fruitflygenetics/flash1.html Notice the difference in the dominant wild type and recessive vestigial wings. Cross the parent generation and then cross the F1 generation to see result in the F2 generation Table 1

F2 Generation

Wild Type Vestigial Winged 1. Hypothesis: What is the genotype of the F1 generation (parents of F2) and how do you predict that vestigial wings are inherited (autosomal or sex linked)

2. Chi Square Analysis: show your chi square analysis in the space below.

Type

Observed 

Expected 

Wild Type Vestigial  Total

3. Results: Was your predicted hypothesis of inheritance correct of not? (accept or reject chi-squared)  

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C. Cross 2: White Eyed Female x Wild Type Male: http://www.biologycorner.com/fruitflygenetics/flash2.html Notice the difference in eye color.  Mate the parent generation.  Then mate the F1 generation and record F2 below.  F2 Generation

Expected

Wild Type Males White eyed Males Wild Type Females White Eyed Females

Hint: make your hypothesis and punnet square before you can calculate the expected

1. Hypothesis: What is the genotype of the F1 generation and how do you predict eye color is inherited (autosomal, sex linked or something else). Show your punnett square.

2. Chi Square Analysis: show your analysis below:  

3. Results: explain your accepting or rejecting in the space, what does that mean and what might explain the results if you rejected?

D. Cross 4: Wild Type Female x Sepia Eyed, Vestigial Winged Male:

http://www.biologycorner.com/fruitflygenetics/flash3.html

Directions: Note what the parent flies look like (differences in wings and antennae) Mate the 2 parents flies. Notice that the F1 generation all look alike, showing only the dominant trait. Them make the F1 generation and count the F2 for the table below.

F2 Generation observed

Hint: this table ignores mmales and females and groups all genders of each trait. This could be done differently if predicting a sex liked trait. You may want to create another column for your predictions

1. Hypothesis: What is the genotype of the F1 generation parents and how is aristapedia and vestigial wings inherited (autosomal or sex linked).

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2. What is the predicted phenotype ratio for this type of dihybrid cross for 2 traits?

3. Chi Square Analysis: show work

4. Explain your results: was your predicted hypothesis of inheritance correct of not? If not, what might explain the error?

5. Keep in mind these are predictions only. If you predict a certain type of inheritance and your chi-square calculation shows there is a significant difference, meaning your punnett square prediction is wrong. What can explain this?

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When finished, read about Genetic Linkage and Genetic Maps http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/L/Linkage.html

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