M. Harley Wilkinson
4.04B- AP Lab 7: Genetics of Organisms
Introduction
The fruit fly is a simple organism that is commonly used in genetic studies because it simple
food requirements, occupies little space, is hardy, completes its life cycle in about 12 days at
room temperature, produces large number of offspring, can be immobilized readily for
examination and sorting, and has many types of hereditary variations that can be easily observed.
The fruit fly has only four pairs of chromosomes, and they are easily located. The fruit fly exists
in stock cultures that can be obtained at the ready, and there is a wealth of knowledge about its
genes from approximately 50 years of study.
Statistics are used to determine if differences among groups are significant, or if the result of a
predictable error. The most frequently used statistical test to determine whether data obtained
experimentally provide a good fit or approximation to the expected or theoretical data is the chisquare test. The chi-square can be used to determine if deviations from the expected values are
due to chance alone, or to some other circumstance.
Methods
Using the virtual lab, practice immobilizing and sexing flies. Examine these flies and note the
characteristics of their eyes, wings, bristles, and antennae. Use virtual flies and distinguish male
from female flies.
Next, using pairs of experimental flies, record the cross number. This number will serve as a
record as to which cross you have obtained. These flies are the parental generation (P) and have
already mated. The females should have already laid eggs on the surface of the culture medium.
The eggs represent the first filial, F1, generation.
When the F1 generation hatches and grows into an adult fly, you then need to observe them
very carefully, making sure to separate males and females. Note whether any mutations are
associated with the males or the females. Identify the mutation(s) and give it /them a made-up
name and symbol. Record the phenotype and symbol in Table 7.1.
Do the same for the F2 generation, making sure to record the mutation(s) into Table 7.2. Then
analyze your data using the chi-square test.
Data and analysis
Parental Generation:
Female- Red eyes
Male- White eyes
Table 7.1: F1 Generation Data
Phenotype
Females
Males
Red eyes
507
495
White eyes
--Phenotype
Red eyes
White Eyes
Table 7.2: F2 Generation Data
Females
469
--
Males
272
242
1) Describe and name the observed the mutation(s).
In the F1 generation, the phenotype for the fruit flies had a 100% showing of the wild type,
red eyes.
2) a Write hypothesis that describes the mode of the inheritance of the trait(s) you studied. This
is your null hypothesis (as described in the Statistical Analysis Section.)
The F1 generation will consist only of the red eye phenotype. The F2 generation will consist of
a 2:1:1 phenotype.
3) Refer to a textbook and review Punnett Squares. In the space below construct two Punnett
squares to predict the expected results of both the parental and F1 crosses from your null
hypothesis.
Parental Cross
Xr
Y
R
Rr
X
XX
XRY
R
RR
X
XX
XRY
r
r
X
Xr
XR
XR
X
XrXr
XrXr
XRXr
XRXr
F1 Cross
XR
XRXr
XRXr
XRXR
XRXR
Y
XrY
XrY
XRY
XRY
Y
XrY
XrY
XRY
XRY
4) Refer the Punnett Squares above. In the box below record the expected ratios for the
genotypes and phenotypes of the F1 and F2 crosses in the experiment.
Expected Genotypic Ratio
Expected Phenotypic Ratio
F1
1:2:1
1:0
F2
1:2:2:2:1
5:3
5) Do the actual results deviate from what was expected? If so, explain how.
The actual results stay true to the expected. Their variations were slight, but not enough to be
considered. Such as in flipping a coin, theoretically, if you flip it 100 times, it will land on
heads 50 of those times. While in actuality, it may land on heads 59 times.
6) From the results, describe your cross.
Is the mutation sex-linked or autosomal?
Sex-linked
Is the mutation a dominant or recessive?
Recessive
Is the cross monohybrid or dihybrid?
Dihybrid
7) Are the deviations for the phenotypic ratio of the F2 generation within the limits expected by
chance? To answer this question, statistically analyze the data using the chi-square analysis.
Calculate the ci-square statistic for the F2 generation in the chart below. Refer to the critical
values of the chi-square (x2) distribution table to determine the p (probability) value that is
associated with your x2 statistic.
Phenotype
#Observed
#Expected
(o-e)
(o-e)2
(o-e)2/e
(o)
(e)
Red Eye
741
614.375
126.625
16033.8906
26.097891
White Eye
242
368.625
-126.625
16033.8906
26.097891
2
X=
69.594371
a) Calculate the chi-square value for these data.
(a.i.1)
How many degrees of freedom are there?
1
(a.i.2)
Chi-square(x2)=
69.594371
(a.i.3)
Referring to the critical values chart, what is the probability value for this
data? 12.88%
b) According to the probability value, can you accept or reject your null hypothesis? Explain
why.
You must reject the null hypothesis because this experiments data concluded a 12.88%
variability rate. This may have been caused by mutations of the flies, and may have been
different under other circumstances.