Download AP Biology Virtual Fly Lab Assignment:

AP Biology Virtual Fly Lab Assignment: NAME:____________
Due:___________________Assigned:______________
You must complete this in order to do Chi-Square practice on Monday.
PART I. Read pp 269-275 in our textbook.
Summarize these figures:
15.2
15.3
15.4
15.5
PART II. Directions: Go to Lab Bench (The Biology Place/Pearson)
http://www.phschool.com/science/biology_place/labbench/index.html
Genetics of Organisms (Virtual Fly Activity)
A) Do the complete activity
B) After completing Case Study 1 and Case Study 2. answer questions 1 through 5 below, then
go on to the Lab Quiz and follow the instructions below.
1.) What is the expected ratio of red eyes to sepia eyes in fruit flies?_________
2.) In a sample of 300 F2 offspring, what are the expected ratios for red eyes: sepia
eyes?________________:________________________
3. ) What is the formula for Chi Square?
4. ) To determine if my Chi Square value is significantly different than expected, I then determine
the Degrees of Freedom. What (numerically) is the Degrees of Freedom ( df) for this particular
character? ( eye color)____________________
5) Practice Problem: In an experimental cross of fruit flies, the parents are heterozygous for eye
color. The expected ratio of red to sepia eye color is 3:1 in the offspring.
( +se X +se ) (+ = red; se = sepia ).
Our null hypothesis: There will be no statistically significant difference between the observed results
of our experiment and the expected results. **
The actual results of this genetic cross are:
250 with red eyes and 50 with sepia eyes.
Is this statistically different than expected? We expect a _____:_____ Red : sepia eye ratio.
(calculate the Chi Square value, then determine the degrees of freedom, then consult a Critical
Values Table.) Is your Chi Square value less than this Critical Value? ___________What
does this mean?____________________________________________
Compare the chi-square value obtained with the Ch1 Square Critical Values Table below for p =
0.05.
Degrees of freedom (df)
2
3
4
5
Probability (p) 1
0.05
3.84 5.99 7.82 9.49 11.1
0.01
6.64 9.21 11.3 13.2 15.1
0.001
10.8 13.8 16.3 18.5 20.5
*Chi Square Note: The actual results of an experiment are unlikely to match the expected results
precisely. But how great a variance is significant? One way to decide is to use the chi-square (x2) test.
This analytical tool tests the validity of a null hypothesis, which states that there is no statistically
significant difference between the observed results of your experiment and the expected results. When
there is little difference between the observed results and the expected results, you obtain a very low
chi-square value; your hypothesis is supported.
C ) Lab Quiz: ( a copy of this is below). This is tricky—dihybrid cross. Expected phenotype
ratios would be the same as Mendel’s observations (p. 253 of our text).
Take the quiz; check some of the incorrect answers so you can see the explanations –
even if you know the answer the first time!)
For question 3, I want to see all your work-so construct a table and show your
calculations.
Lab Quiz
1. On the basis of the results shown in the table, which statement is
most likely true?
a.
b.
c.
The genes for red eyes and normal wings are linked.
The gene for no wings is sex-linked.
The gene for red eyes and the gene for no wings are both
dominant.
NOTE:
Answers to questions
may be lost when you
proceed to the next
screen. Print this
screen if you need a
record of your
answers.
d.
The gene for eye color is inherited independently of the
gene for wings.
e.
The F1 mates were both homozygous for both eye color
and wings.
2. If the parents were both heterozygous for eye color and wings,
what phenotypic ratio would you predict for the offspring if these
traits are not linked?
a.
b.
c.
d.
1 red eyes/no wings
1 red eyes/normal wings
1 sepia eyes/normal wings
1 sepia eyes/no wings
9 red eyes/normal wings
3 red eyes/no wings
3 sepia eyes/normal wings
1 sepia eyes/no wings
3 red eyes/normal wings
1 sepia eyes/no wings
1 red eyes/normal wings
2 sepia eyes/normal wings
1 red eyes/no wings
2 sepia eyes/no wings
Sorry. The correct answer is b. If there were linkage, choice a would
be correct, but when two traits sort independently, the offspring of
heterozygous parents will show the traits in a 9:3:3:1 ratio.
3. Based on the hypothesis that this is a dihybrid cross, with the two
genes unlinked, calculate using the data in the table of observed
phenotypes.
a.
b.
c.
d.
6.04
7.81
4.977
24.0
4. How many degrees of freedom are there for these data?
a.
b.
c.
1
2
3
d.
4
5. Compare the chi-square value obtained in Question 3 with the
Critical Values Table below for p = 0.05. Which of the following
statements would be true?
Degrees of freedom (df)
2
3
4
Probability (p) 1
5
0.05
3.84 5.99 7.82 9.49 11.1
0.01
6.64 9.21 11.3 13.2 15.1
0.001
10.8 13.8 16.3 18.5 20.5
a.
b.
c.
d.
Since the calculated value for chi-square is less than
7.82, the results support the hypothesis that the parents
are heterozygous for two unlinked traits.
Since the calculated value for chi-square is less than
7.82, the results support the hypothesis that eye color and
wings are linked.
Since the calculated value for chi-square is less than
7.82, the results are inconclusive. The experiment should
be repeated.
Since the calculated value for chi-square is so large, the
variations from the expected are excessive. The
experiment should be repeated.
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