1. Fruit Fly Drosophila melanogaster experiment
AP Biology – 2018 Lab
Dihybrid Cross and Sex-linked cross

2. Find a buddy for the fruit fly experiment
Go pick up two vials, two foam caps, two stickers and place them on your vial in the center of your vial
Watch your teacher demonstrate how to make a vial with media
Make a vial with media, don’t forget to put only about 4-5 grains of yeast on the top of the media.
3. Now pick up a booklet of fruit flies and read the pages indicated until your teacher has you come up to get your flies and put them in your jar. Before you put them in your jar. Look at them under the microscope. Make sure to write the NUMBER of each of your males and females on your jar and which have white eyes and which have wild(red) eyes.

3. Take a booklet on Fruit flies and read/take notes on
Page 8, and 9 Life cycle and anesthetizing – HOW LONG DO YOU LEAVE IN WAND of fly nap? IMPORTANT – sleep not death
Page 11 sexing and look at back of pamphlet
Look at page 15, 16 and 17 on phenotypes
Skim through the rest of the booklet to look at types of crosses and other information about Drosophila

4. Let’s look at a fruit fly crossx
Wild eye, vestigial wing
Sepia eye/wild wing P1
F1: all wild
F2 are all: 9:3:3:1

5. Get your fruit flies and your booklet
Take out a sheet of paper to record your data for your fruit flies
Male red Male white Female red Female white
Create a chart and use tally marks.

6. Sex-linked cross Wild eyes vs. White eyes
Parents XRXR x XrY
or XRY x XrXr
F1 Cross What is expected?

8. Male vs Female

9. Determining sex Female notice clear bottom, larger Male Dark end
On bottom

10. Class Results of Red eyed fem and white eyed males
Group Name
Parents were Cross of Red eyed females with white eyed males XRXR x XrY
Red eye female
Red eye male
White eye female
White eye male
Wk 1
Wk 2
Jade/Noah/
Sean 16 24 17 20
Abby/Reece 14 26 13 33
Liz/Skylar 15 79 56
Trinity/Raygen 18 30

11. Class Results of Red eyed females and white eyed males
Parents are cross of White eye female and red eye male
XrXr x XRY/XrY apparently white eye males got in here 
Group Name
Red eye female
White eye female
Red eye male
White eye male
Wk 1
Wk 2
Wk2
Brandon/
Jordan 1 10 2 22 20 17
Eleanor/Klay/
Lauren 8 4

12. Dihybrid cross F2 results Tally your marks then share results
Group Name
Red eyes, wild wing
Red eyes, vestigial wing
Sepia eyes, wild wing
Sepia eyes, vest wing
Day 1
Day 2
Day 3
Reece &
Abby 55 8 7 22 4 2 20 10 1
Brandon
Jordan 34 5 14 11 9 3
Trinity
Raygen 18 12 6
Klay Lauren
Eleanor
Liz &Skylar 35 19
Noah Sean
Jade 49 17

13. Write up for Fruit flies: Focus on dihybrid but discuss the X-linked cross in your analysis/results, conclusion.
Problem/Question: Will a dihybrid cross of sepia/vg mutant parents crossed with wild result in the expected ratio of 9:3:3:1 and meet the null hypothesis.
Hypothesis: Yours – might be the the NULL hypothesis.
Materials:
Procedure:
Data tables/GRAPH,
Analysis/Results: Show your math for Chi Square
Conclusion: Follow writeup directions for Conclusion(3 paragraph approximately.)

14. Now Conduct the Analysis:
To determine null hypothesis value take the total number of flies and divide by 1/16, 3/16, 3/16, 9/16 to get the expected

15. 2018 RESULTS add all your x2 values
Phenotypes
observed
expected
o-e
(o-e)2 X2
Wild
Red eyes/ normal wings
Red eye
Vg wing
Sepia eye

16. How many degrees of freedom? #phenotypes – 1 = degrees of freedom,
look under the .05 column
CHI-SQUARE DISTRIBUTION TABLE
Accept Hypothesis
Reject Hypothesis
Probability (p)
Degrees of
Freedom
0.95
0.90
0.80
0.70
0.50
0.30
0.20
0.10
0.05
0.01
0.001 1
0.004
0.02
0.06
0.15
0.46
1.07
1.64
2.71
3.84
6.64
10.83 2
0.21
0.45
0.71
1.39
2.41
3.22
4.60
5.99
9.21
13.82 3
0.35
0.58
1.01
1.42
2.37
3.66
4.64
6.25
7.82
11.34
16.27 4
1.06
1.65
2.20
3.36
4.88
7.78
9.49
13.38
18.47 5
1.14
1.61
2.34
3.00
4.35
6.06
7.29
9.24
11.07
15.09
20.52 6
1.63
3.07
3.83
5.35
7.23
8.56
10.64
12.59
16.81
22.46 7
2.17
2.83
3.82
4.67
6.35
8.38
9.80
12.02
14.07
18.48
24.32 8
2.73
3.49
4.59
5.53
7.34
9.52
11.03
13.36
15.51
20.09
26.12 9
3.32
4.17
5.38
6.39
8.34
10.66
12.24
14.68
16.92
21.67
27.88 10
3.94
4.86
6.18
7.27
9.34
11.78
13.44
15.99
18.31
23.21
29.59

17. One more helpful hint as you writeup your lab
When reporting chi square data use the following formula sentence….
With degrees of freedom, my chi square value is , which gives me a p value between % and %, I therefore my null hypothesis.
This sentence would go in the “results” section of your formal lab.
Your explanation of the significance of this data would go in the “discussion” section of the formal lab.