Teacher Notes for Virtual Fruit Fly Genetics

TEACHER NOTES FOR VIRTUAL FRUIT FLY GENETICS

TIME TO COMPLETE LAB: One 40 minute class period. Some additional time may be necessary to perform the data analysis and answer the questions.

TARGET GRADE LEVEL: 7th – 10th grade

OBJECTIVE/MAJOR CONCEPTS:

·  Be able to identify male and female fruit flies.

·  Learn to use a Punnett square to predict the outcome of a genetic cross.

·  Understand how to compare predicted results and observed results.

PREPARATION:

Some basic knowledge of genetics and how parent flies pass alleles to their offspring. This will help the students understand how to use the Punnett square and how it shows the possible allele distributions in the offspring.

SAMPLE DATA:

EXPERIMENT 1

Parent Flies: Sex _Male Phenotype Wild-normal wing Sex _Female Phenotype _Vestigal wings

Results of Genetic Cross - Experiment 1
Phenotype / # of flies with phenotype (male + female) / % phenotype
(Total # phenotype ¸ 20 flies) X 100
Wild-normal wing / About 10 / About 50%
Vestigal / About 10 / About 50%

EXPERIMENT 2

Parent Flies: Sex _Male Phenotype _Wild-normal wing Sex Female Phenotype _Wild- normal wing

Results of Genetic Cross - Experiment 2
Phenotype / # of flies with phenotype (male + female) / % phenotype
(Total # phenotype ¸ 20 flies) X 100
Wild-normal wing / About 15 / About 75%
Vestigal / About 5 / About 25%

ANSWERS TO QUESTIONS

1. Fill in the chart.

2. Using the data in the chart, how do the percentages for the actual genetic crosses compare to the results you predicted with a Punnett square? Explain.

The results from the genetic crosses should be close but will not be exactly the same as the ones based on the Punnett squares. Punnett squares only PREDICT the chance that things will happen. In the real world, there will be some variation.

3. How could we get the percentages in our genetic crosses (the offspring of our parents) to be closer to what our Punnett squares say they should be?

The larger the sample (the number of offspring) the closer the results will come to what is predicted in the Punnett squares. Although 20 may seem like a large number of offspring, in the world of samples, it is a small amount. If we did a sample of 200 the results would be much closer to what is predicted.

4. Based on the results from the Punnett square, each offspring should receive two different alleles for wing type.

a. What are the two different alleles that were involved in this lab.?

N and n

b. What type of wing is represented by each allele?

N = normal wings

n = vestigal wings

c. When a fly has one of each of these alleles, why do you see only one phenotype?

The N allele is dominant, and masks any effect of the n allele, resulting in a fly with the long wing phenotype.

5. Why have scientists use fruitflies used for genetic research?

Fruitflies were chosen for many reasons. They have inherited traits that are fairly easy to see. They are small and easy to maintain. They have a short live cycle and produce lots of offspring. Today organisms like the nematode, C. elegans, are often used because they are even smaller and have even shorter life cycles.

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