Dana J. Koczur
Cellular Biology
April 26, 2012
“Hereditary Links Between Traits in Fruit Flys”
Introduction:
Fruit flies or Drosophila Melanogaster (Figure 1)
is an important organism in the development of biology.
There are many benefits for using fruit flies for this
experiment. The life cycle of a fruit fly is very short
making them easy to study and track the heredity. The
Figure 1: Fruit Fly or Drosophila
Melanogaster.
average life of a fruit fly is 30 days. This life cycle is greatly affected by the temperature of the
environment if it is below 60 degrees or above 85 degrees. Females lay upwards of 400 eggs in
ten days. There are four stages in the life cycle of the fruit fly: egg, larva, pupa, and adult (Figure
2). It takes two weeks to mature into an adult from an egg after the eggs are laid in fruits or other
sugary, organic, foods that have plenty of nutrition. Eight days in the egg and larval stages, and
six days in the pupal stage absorbing nutrients from the food. Twenty-four hours after the egg is
Figure 2: Stages of the fruit fly’s life cycle from egg to adult.
laid, the larva hatches. The larva has two molting periods, during which the cuticle, mouth,
hooks, and spiracles are shed and changes into different colors throughout the transformation.
After transforming into an adult fly the females will be able to reproduce in 48 hours. The
differences between males and females are easily distinguishable (Figure 3). Males are smaller,
have 5 abdominal segments, dark hair like projections
on their legs that are called sex combs. They have two
claspers under their abdomen and the tip of the
abdomen is rounded. The difference in females is they
have claspers and 7 abdominal segments and their
abdomen is pointed at the tip. By studying these flies
Figure 3: Visual differences between male
and female fruit fly.
we can accumulate lots of data and multiple generations
in a short period of time. Also, the mutations are easily studied because of the size of the fly
(Flagg, 2005).
Some of the first scientists to use fruit flies are Charles W. Woodworth, the scientist with
the original idea to use fruit flies for hereditary experiments. Thomas Hunt Morgan is also
known for the basis of heredity such as mutations and the importance of the gene, by using the
fruit fly in his experiments. The results of these experiments showed the fruit fly was easily
reliable because of the continuous and recurring mutations. This helped provide information for
heredity such as: sex-linked inheritance, multiple alleles, and gene mapping. In our lab we are
examining the genetic crosses demonstrating dominant and recessive traits, and sex linkage are
being examined (Almadi, 2012).
Hypothesis:
Eye color trait is a sex-linked trait. The hypothesis was tested by studying four vials of
fruit flies to determine the physical differences and effects of the two parents on their offspring.
To develop our punnett squares we first determined phenotypes and genotypes (see figure 4).
The Punnett squares information (see figure 5) also correlated directly with the hypothesis when
crossing the males and females with different mutations and traits (Almadi, 2012).
Phenotype
Genotype (sex chromosomes)
White eyed male
X-Y
White eyed female
X-X-
Red eyed male
X+Y
Red eyed female
X+X+
Figure 4: The Genotypes for each different male and
female.
Null: There will be no difference shown with the sex linked autosomes.
Alternative Hypothesis: There will be no difference shown in the sex linked autosomes
(see figure 6).
From our determined hypotheses we predict that by crossing parents with mutations will
produce offspring with mutations. This prediction also depends on what type of offspring. In our
lab the male offspring will be the same as the mother but 50/50 if the mother is homozygous.
This lab is important because it helps us understand how genes can be passed on from one
organism to its offspring. This also includes mutations studied in our experiment.
X-
X-
X+
X-X+
X+X-
y
X-Y
X-Y
X+
X+
X-
X+X-
X+X-
Y
X+Y
X+Y
X+
Y+
X+
X+X+
X+X+
Y
X+Y
X+Y
X-
X-
X-
X-X-
X-X-
Y
X-Y
X-Y
Figure 5: Hypothesis punett outcome of the cross if it is sex-linked.
R
O
R
RR
OR
O
RR
OO
R
O
r
Rr
Or
r
Rr
Or
r
r
R
rR
rR
O
rO
rO
r
r
r
rr
rr
r
rr
rr
Figure 6: Alternative Hypothesis: If the eye color allele was located on an
autosome and NOT a sex chromosome (no sex linkage). R= dominant, r =
recessive.
By doing this experiment we are approaching the use of fruit flies to study heredity
carefully studying hundreds of flies with the information from every individual fly included. This
allows us a large number of examples in a short period of time. We are gathering data that will
tell us whether our hypothesis that their heredity is based off of sex-linked genes.
Methods:
The first procedure in our experiment was to become acquainted with the fruit fly or
Drosophila. The experiment studied the anatomy of the fruit
fly to make sure the differences between male and female
fruit flies were distinguishable. We also learned different
mutations that can occur. These mutations include different
wing shapes and eye colors to name a few (Figure 7). We also
Figure 7: Different fruit flies
including males and females, red
eyes and white eyes.
learned about the fruit fly’s life cycle from an egg to an adult which only take about 8 days.
Another important factor is learning how to knock out the flies for observation using Ether-ators
though we didn’t use the procedure in the class (Almadi, 2012).
Next we determined the number of flies we were given in our predicted genotypic ratios.
This helped us develop our sex chromosome model. We first had a predicted model based on the
cross of a red eyed heterozygous female with a red eyed male and recorded our expected
outcome for 500 offspring and calculated our chi-square value and punnett squares to show data.
Our expected outcome is ½ red eyed females, ¼ red eyed males, and ¼ white eyed males.
To calculate the chi square values we use the proper formula (Figure 5) for each of the
four different possible offspring and correlate it with the Chi Square and Probability Chart. Now
that we have a predetermined model of the genetic outcome we
could count the flies ourselves that correlate the data with the
punnett squares (figure 8). To do this we counted each fly and their
specific traits into separate possible results with the four vials for
each specific cross. In this experiment we are testing the gene for
Figure 8: Chi Square
Formula
eye color on the X chromosome. After counting out all four vials we put our data in a table and
determined the Chi-square values. Then added our data to the entire class to get an overall view
of the data we all collected showing us that the traits passed on in the flies is sex-linked (Almadi,
2012)
Results:
The results of the experiment showed that our hypothesis that mutations in fruit flies are
sex-linked was correct. Each cross was important in determining this because to understand how
traits are passed on, studying every single possibility is essential. Each different outcome shows
us what can or can’t be passed on to offspring. Knowing what cannot be inherited is just as
important as knowing what can be inherited. Vial 2 is a good example of this. Vial 2 showed
how the males look like their fathers and the females look like their mothers (Almadi, 2012).
Figure 9: Observed and expected fly numbers for 4 different experimental crosses for the class
information.
Females
Vial
Red
266
313
276
2
1
2
3
4
Actual
White
0
6
5
34
Red
271.5
297
281.5
0
Males
Expected
White
0
0
0
330
Red
277
7
279
2
Actual
White
0
268
3
314
Expected
Red
White
271.5
0
0
297
281.5
0
0
330
Figure 10: Chi-square information: calculated and critical value for class information.
Vial
1
2
3
4
Chi-square calculated
0.22
3.66
0.13
1.212
Chi-square from table
7.815
7.815
7.815
7.815
Accept or reject null hypothesis of no difference?
Reject
Reject
Reject
Reject
Discussion:
The data collected from this experiment matches our hypothesis and proves that sexlinked traits are passed on in fruit flies. Our results show that with the information from the class
for each vial shows the outcome when a red eyed heterozygous female and red eyed male fruit
fly are crossed. The results show that the traits from each parent are can result in the four
different options for flies. Vial 1 had all red eyes for females and males. Vial 2 had most red eyes
for females and most white eyes for males. Vile 3 has most red eyes for females and most red
eyes for males. Lastly vile 4 had very few red eyed females and white eyed females and mostly
white eyed males. This information from the class correlates with the information expected
proving that the color of the eyes is a sex linked trait.
Some of the problems that we ran into were that some of the flies were cut in half when
we were counting and studying the vials so we had to count the heads only. Also the flies would
blow away if you weren’t careful or breathed on them. It was hard to count the flies if they were
piled up and losing track of the number of flies was easy as well.
Conclusion:
In conclusion, the importance of these experiments is to learn about heredity and how
genes and traits are passed to offspring. This can show us many things such as the genetic
crosses demonstrating dominant and recessive traits, and sex linkages between traits. This is just
the opening into determining many new things about our genes and heritage that we didn’t
understand before.
References:
Alemadi S. and Brisch E. 2012 Cell Biology Lab III: Genetics I. Moorhead (MN):
Minnesota State University Moorhead.
Flagg R. 2005. Carolina Drosophila Manual, Carolina Biological Supply Comp.