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Alcohol Tolerance in Drosophila and You

Theresa M. Peters



Type of entry:

  • Lesson/class activity

Type of activity :

  • Hands-on
  • inquiry lab
  • group/cooperative learning

Target audience:

  • Life Science
  • Biology
  • Genetics


Background information:

What question does this activity help students answer

At a molecular level, this activity attempts to reinforce a student's understanding of how a gene controls the production of an enzyme. From an ethical standpoint, the activity addresses the issue of genetic testing and whether an individual should be penalized for their genetic make-up.

Notes for teachers:
This activity can be incorporated into several areas--health, bioethics, genetics. I offer it as part of my sophomore biology course as a means of integrating some health issues into the curriculum. Consisting of both a laboratory experiment and an in-class debate, I have found that this is one of my students' favorite activities.

Required of students:
The laboratory part of this activity requires that the students have a basic understanding of alcohol and its effects on the body, protein synthesis, and Mendelian genetics. Moreover, the students will need to watch their flies over a 24 hour period, which will require them to take the flies home for a night.

Class time needed:
The activity will take up to three class periods, depending on how much time the instructor allows for student exploration. The actual laboratory takes 20 minutes to prepare. A period of 20 minutes the following day gives ample time to discuss class data. The ethics exploration will take up to 30 minutes for small group discussion.


Abstract of Activity

If you open any magazine or newspaper these days, you can typically find an article on the most recent genetic breakthrough. While most of these discoveries are on a genetic disease, more and more studies are implicating DNA's involvement in such areas as mental disorders, sexual orientations, and addictions. At a molecular level, genes have been found to influence alcohol tolerance in Drosophila melanogaster. In 1990, Rutgers State University offered a summer program in conjunction with the National Teachers of Biology that included a unit on Drosophila. Several activities in this unit studied the Adh gene, which controls the production of alcohol dehydrogenase (ADH) enzyme. Flies possessing the dominant Adh gene have them ability to oxidize ethanol:

     ADH
NAD+  + alcohol --------> NADH + aldehyde (or ketone) + H+

ADH- flies cannot break down the ethanol they consume, leading to visible inebriation in their behavior and flying, ultimately leading to alcohol poisoning.

In this activity, students develop and run a laboratory comparing alcohol tolerance in flies with and without the ADH enzyme. Following the experiment, they participate in a fictional court case involving denying humans possessing a malfunctioning Adh gene the right to purchase alcohol.


Lesson/activity

Materials

Fruit flies:
As only one vial of each type of flies is sent, place your order two months prior to the activity date. It takes about one week for the flies to hatch upon arrival, and two weeks for each subculture to increase the fly population to the reach the size necessary for classroom use.

Fly vials:
Enough for subculturing the fly strains and at least one vial and sponge for every lab pair.

Other materials:
Instant fly media, cotton balls, stirring rods, pipettes/sm. graduated cylinders, cheap wine, paint brushes, refrigerator or Flynap, student handout on courtroom scenario.


Activity

Instructor Information

Have the flies presorted into vials of 20 or so before lab. These flies can be anesthetized when class starts. Chilling flies requires 5-10 minutes before they are manageable. Keeping them on ice afterwards also slows their revival. Other means of anaethizing the flies are using Fly nap, or C02 exposure (alka seltzer tablets or dry ice). Use accespted safety guidelines when dealing with any controlled substance, including alcohol.

The activity begins best with a discussion of alcoholism and its affects on the body and on society at large. When a discussion of the causes of alcoholism ensues, introduce the students to flies lacking the Adh gene and to some of the background on the condition. Then propose the question "How would you test for alcohol tolerance in fruit flies?" Guide the students to design a laboratory to answer the question. The following protocol has been very effective:

1. Each person should obtain an empty vial, 3-4 cotton balls, and a stirring rod.

2. Each person should wedge the cotton balls in the bottom of their vial.

3. Working in teams of four, choose which set up you will perform.

 Person A: ADH- flies in water     Person C: ADH- flies in wine
 Person B: ADH+ flies in water     Person D: ADH+ flies in wine

4. Persons A and B should add 5 ml of water to their vial. Persons C and D should add 5 ml of wine to their vial. Each cotton ball should be soaked but not submerged. Using the stirring rod, tap down the cotton balls to wedge them in place and to drain off excess fluid. Test the cotton ball's security by inverting the vial.

5. Dry the inside walls of the vials. (Flies can drown in drops of fluid)

6. Use a piece of tape and a marker to label the vial with your name, type of flies and whether water or wine is included.

7. Obtain the vial of chilled flies assigned to your lab team. The flies in the vial should not be moving. If the flies wings or legs appear to trembling they should be chilled further. As soon as the flies warm up, they wake up and fly away.

8. Open the chilled vial and pour the flies onto a piece of paper. Using the paint brush, gently sweep 5 flies of the strain you require into your vial. Stopper the vial, but leave the vial on its side so the "sleeping" flies will not drown in the wet cotton.

9. When the flies revive, turn the vial upright. If less than 3 flies recover, obtain more.

10. Observe the flies over the next 24-hours at the times listed below. Make a data table of your observations. Note all behaviors observed.

15 minutes
30 minutes
60 minutes
4 hours
8 hours
whenever you wake up

After the students have studied their flies for the 24- hour period a discussion of class data comparing results should occur. Students need to be sure to differentiate fly death due to alcohol poisoning versus other factors. Following this discussion a fictional court case is passed out on alcohol susceptibility. Each student group obtains a "courtroom brief" which includes the some background information on alcoholism, the proposed law, and discussion questions all in a folder. The students are to read through the court case and in their small groups discuss the law and its implications, taking any notes on their ideas. Their homework that night is to make a conclusion based on their discussion and turn it in with a paragraph supporting their rationale. The following day the instructor should mediate a class debate on the proposed law.


STUDENT INFORMATION

Court Case 24390AQ-3
Mandatory Alcohol Abstinence Law

Case Background:
Alcoholism is a serious problem in the United States. Long term use of alcohol leads to many known problems. Alcohol is known to damage neurons when taken in large amounts, leading to permanent peripheral nerve damage. Cirrhotic livers result from scar tissue formation after liver cell death. Liver failure is 9th leading cause of death in the United States. Habitual alcohol use has been implicated in reproductive, hormonal, and immune problems. Constant use also leads to ulcers in the stomach, esophagus, and intestines. Hypertension and enlarged hearts are often found in alcoholics. It is estimated that between 10-15 percent of Americans are alcoholics, thus subject to suchdamaging affects.

It should be noted that alcohol abuse does not affect the drinker alone. Families, friends, employers, and even strangers are all affected by an individual's drinking. It is estimated that 3 out of every 100 deaths in this country can be tied to alcohol use. For instance in 1990, 19,990 people died in alcohol related car accidents, which is about one half of all automobile deaths. Many examples of physical abuse, acts of violence, and suicide can be linked to alcohol abuse. Estimates of $25 billion worth of damage occur each year at work sites due to employees under the influence. Moreover, there are more than 50,000 babies born with fetal alcohol syndrome each year, resulting in children with specific facial defects and often mental retardation.

As with other addictions, alcoholism's causes and cures are not clear. Being raised in an alcoholic household implies environmental factors at work, such as social, cultural and peer influences. However, in light of evidence from twin and adoption studies, a genetic component has also been implicated. While not as simple as the Adh gene in fruit flies, a complex polygenic predisposition to alcoholism may exist in humans.

Proposed Law
All applicants for a drivers license must undergo a genetic test for alcoholism susceptibility. Those individuals who possess multiple (3-4) alleles for a malfunctioning Adh gene will be issued a special license. The alcoholism susceptibility license will possess hologram stating "ineligible to purchase alcoholic beverages" making it against the law for any such individual to buy alcohol. Any such person caught purchasing alcohol will have their license suspended for two years and serve a two month jail term. In addition, any individual who sells alcohol to a susceptible individual will be fined $5,000. Any individual who purchases or gives alcohol to said person will face a 1 month jail term.

Discussion Questions

1. How might the lack of the Adh gene product lead to alcoholism? Is this based on sound science?

2. Is this law constitutional? Will stand up in a civil rights court? Consider the recent smoking laws.

3. Does this law discriminate against one's genotype?

4. Does this law solve all causes of drunk driving?

5. Is the law enforceable?


Method of Assessment

The students are required to turn in a formal laboratory report on the fly activity, including an introductory statement, procedure, data tables and conclusion. In the courtroom activity, students turn in their judgment on the fictional law and at least one paragraph supporting their judgment.


Extension

These activities have many areas that can be explored further. In part A, I have had students test the alcohol tolerance of other strains of Drosophila, like white eyed flies or flies trapped from the environment. One could also explore different alcohols or concentrations to see how fast the ADH- flies become inebriated. Another area to be explored is a molecular comparison of the ADH- and ADH+ flies through DNA extraction techniques and gel electrophoresis or through use of a spectrophotometer and nitro blue tetrazolium, an ADH histochemical stain.

I have also enhanced these activities through various audiovisual additions. When discussing alcohol and its affects on the body I use the Health EDCO slide series which illustrates various human organs of alcoholics. Moreover, I have shown my students the 1980's 60 Minutes Program titled "The Perfect Baby" which discusses the ramifications of genetic testing in regards to genetic diseases such as cystic fibrosis and Tay Sachs.


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