Izabella Plotnick
Katherine Sampuda
BIO 3251-001
September 26, 2014
Determining Inheritance Patterns through Mating Drosophila melanogaster
Abstract: Patterns of inheritance are instrumental to understanding the world of genetics; there
are many routes to take when analyzing inheritance patterns and many species that can be used to
develop this understanding. One such species is the Drosophila Melanogaster, or the fruit fly. A
question then arises: what inheritance patterns are to be looked for, and how will they be looked
for? Focusing on two specific traits, eye color and wing type, an experiment was conducted to
determine what inheritance patterns are prevalent to address this question. With the
understanding that the white eye color is a mutant trait, and that apterous wings are also a mutant
trait, a hypothesis was formed, which states that both of these mutant traits are recessive, and
more importantly, the white eye mutant trait is x-linked recessive while the apterous wing mutant
trait is autosomal recessive. After mating a parent generation of a wild-type female, (redeyed/normal winged), and a white-eyed, apterous-winged male, and interpreting the data
resulting from that cross, the hypothesis stands true. However, when pushing forward with the
experiment and conducting two different crosses, one normal female with one mutant male and
vice-versa, and interpreting the data resulting from those two crosses, the hypothesis was not
supported. These two conflicting results led the experiment to an inconclusive outcome. It was at
this point that basic science principle had to be introduced, as it is a known fact that both the
white eye mutant trait is x-linked recessive and the apterous wing mutant trait is autosomal
recessive. With that in mind, the only explanation for this phenomenon led to human error.
Introduction: The species Drosophila Melanogaster is the scientific name for a fruit fly.
Drosophila Melanogaster, through the decades, has been very important for scientific research,
in specifically genetic experimentation and interpretation when in relation to advancing
knowledge of the characteristics of genetic inheritance (L. Charles et. al. 2012). The reason for
why Drosophila melanogaster has been so popular in genetic research is because it is possible to
study giant populations at a time, as a single mating produces hundreds of offspring at a time, it
takes relatively short time for an egg to develop into an adult, only has four pairs of
chromosomes which are easily observed with a microscope, and is relatively inexpensive to
maintain (Beam and Kalumuck). It is the model organism for this experiment in genetics.
Typically, populations of these fruit flies are found among humans in almost all tropical and
temperate locations. Through genetic analysis, Sub-Saharan Africa has been determined to be the
center of diversity for these fruit flies, likely alluding to the location of Drosophila melanogaster
origin (L. Charles et. al. 2012). Drosophila melanogaster are also very important in the study of
genetics because they were the first species to show that chromosomes were associated with
genetic information; this was first discovered by Thomas Hunt Morgan in 1910 (R. Piergentili
2010). Drosophila melanogaster were found, and still are to this day, useful to trace inheritance
patterns. That is why an experiment has been conducted using Drosophila melanogaster, and the
experiment centered around the mutant traits of white eyes and apterous wings, and the question
at hand was whether each of these traits are either dominant or recessive, and whether the genes
for the mutant traits are located on an autosomal (non sex chromosome) or X-linked
chromosome (sex chromosome). An individual with an autosomal-recessive mutant trait is one
that requires two mutant alleles, one from each parent, and has nothing to do with gender (H.
Chial 2008). An individual with an autosomal-dominant mutant trait is one that requires only one
single mutant copy of the mutation-associated gene, and still has nothing to do with gender (H.
Chial 2008). X-linked traits are slightly more complicated. A female with an X-linked recessive
mutant trait must have received a copy of the mutant gene from her father, who also exhibits the
trait, and a copy of the mutant gene from her mother, who is either affected or a carrier (H. Chial
2008). A male with an X-linked recessive mutant trait only receives the mutant copy of the gene
from his mother since males only carry one copy of the X chromosome. On the other hand, a
female with an X-linked dominant mutant trait can either receive a copy of the mutant gene from
her father or mother, whereas a male always receives a copy of the mutant gene from his affected
mother (H. Chial 2008). That being said, even though red-eyes in fruit flies are an X-linked
dominant trait, the overall mode of inheritance is X-linked recessive. The same goes for wing
shape; even though normal wings are an autosomal dominant trait, the overall mode of
inheritance is recessive. Drosophila melanogaster has been crucial in the development of this
information throughout history. When Thomas Morgan discovered, through the use of fruit flies,
that genetic information was related to chromosomes, he was able to connect a direct genetic
relationship between the X- chromosome and the resulting phenotypic trait, eye color in fruit
flies (R. Piergentili 2010). Since that discovery, the fruit fly’s eye color has been the premier
example of a sex-linked trait (P. Guilfoile). The purpose of this experiment is to see first-hand
how this conclusion was ascertained, if eye color is recessive or dominant and to answer
questions about the inheritance pattern in relation to mutations in the wings and eye color. The
experimenters expect to find that mutant eye color trait is truly x-linked, and also hypothesize to
find the mutant eye color trait is recessive since white-eyed flies aren’t as commonly seen. At the
same time, the experimenters expect to find that the apterous wing mutant trait is to be an
autosomal recessive trait because most flies appear to have normal wings.
Materials and Methods: Throughout the entire experiment, the flies were kept in an incubator
at 24 degrees Celsius, except when being handled by the experimenters. To perform the research
necessary for this experiment, 2 vials of flies were obtained. Inside these two vials was a yeast
food medium for the flies to feed on for nourishment. The first vial contained wild-type female
and male flies, and the second vial contained male and female mutant flies. After given the vials,
the flies had to be anesthetized by using FlyNap solution. To put the flies to sleep, a tiny brush
was dipped into the FlyNap solution. After removing the foam caps on top of the vials, the brush
was slowly slipped inside until the flies were noticeably not moving anymore. Once the flies
were asleep, the vials had to be kept on their sides due to premature accidental death that would
be caused by the flies sliding down to the yeast food medium, only if the vials were to be stood
upright. After the flies were noticeably sleeping, the brush was removed from each of the vials,
with the flies being gently removed, and transferred onto a notecard. Once on the notecard, the
flies were placed directly under a dissecting scope, and then sorted into one of four groups:
male/wild-type, female/wild-type, male/mutant, female/mutant. Then 5-10 individuals of each of
the male phenotype were separated. Then different vials of virgin females were obtained in order
to mate with the two different male phenotypes (male wild-type and male mutant). The males
from the wild-type vial were placed in one of the vials containing virgin females, and the males
from the mutant vial were placed in the other vial containing virgin females. After these flies
mated, the adult flies were removed from each vial to prevent the offspring that emerged from
mating with the parents. Once this was done, the F1 generation of flies were obtained from each
of the vials and then examined after anesthetizing them with FlyNap solution again, as done
previously. Once the flies were no longer moving in each vial, they were then transferred onto a
notecard and viewed under a dissecting scope. Using a paintbrush, each fly was gently pushed
into one of four groups; male/wild-type, female/wild-type, male/mutant, female/mutant. After the
sorting process, a new empty fly house was obtained to which the selected males and females
were added. This set up the F2 cross and in two weeks the data was collected for the new
offspring.
Results:
Figure 1:
http://www.drosophilab.com/genetics.html
Figure 1 above, shows the differences between male and female Drosophila melanogaster.
Female flies have many thin black stripes across their bodies, while male flies have a few black
stripes across their bodies, with one stripe being thick in bandwidth.
Figure 2:
http://www.cs.scranton.edu/~kapplerk2/drosophila.php
Figure 2 above, shows the life cycle of Drosophila melanogaster. There are four stages in their
life cycle. The first step is when the “fly” is just an egg. The second step is when the egg hatches
Larvae. The third step is when the larvae grow and become Pupae. The fourth and final step of
their life cycle concludes the pupae. Once the pupae have grown the adult flies emerge.
1. Po: Wild-type females crossed with white-eyed apterous males
F1: Resulting Male population phenotypes
Males
(P)
Wild-Type
Females x w/ap
Males
Column1 Group
1
Group
2
Group
3
Group
4
Group
5
Total
White
eyes/Apterous
wings
0
White
eyes/Normal
wings
0
Red
eyes/Apterous
wings
0
Red eyes/Normal
wings
19
20
38
33
22
132
Males
The chart above show a cross between a White eyed apterous male (xaYa) and a wild type
female (XAXA), and the resulting F1 generation phenotypes for solely males. The data indicates
that all of the males received red eyes and normal wings, and this is because they inherited both
of the dominant copies for these traits from their mother.
2.
Po: Wild-type females crossed with white-eyed apterous males
F1: Resulting Female population phenotypes
Females Wild-Type
(P)
Females x
w/ap Males
Column1 Group Group Group Group Group Total
1
2
3
4
5
White
eyes/Apterous
wings
0
White
eyes/Normal
wings
0
Red
eyes/Apterous
wings
0
Red
eyes/Normal
wings
28
40
33
28
23
152
Females
The chart above show a cross between a White eyed apterous male (xaYa) and a wild type
female (XAXA), and the resulting F1 generation phenotypes for solely females. The data
indicates that all of the females received red eyes and normal wings, and this is because they
inherited both of the dominant copies for these traits from their mother.
3.
F1: White-eyed apterous male crossed with a wild type female
F2: Resulting Eye Colors
White eyed apterous male x normal
female
obs
exp
obs-exp
(obs-exp)2
/exp
red eyed females
78
64
14
196
3
red eyed males
74
64
10
100
1.5
white eyed females
50
64
-14
196
3
white eyed males
54
64
-10
100
1.5
total population: 256
x2= 9.0
degrees of freedom= 3
reject null
hypothesis
The chart above show a cross between a White eyed apterous male (xY) and a wild type
female (Xx), and the resulting F2 generation phenotypes. This information can be seen in the
observed column for each phenotype. In order to perform a chi-squared analysis, the expected
values were calculated based on a 1:1:1:1 ratio created when crossing xY and Xx in a Punnett
square, which was then scaled to the total population of 256. The chi-squared test comes to be
9.0, resulting in a rejected null hypothesis, with the null hypothesis being that the white eye
mutant trait is an x-linked recessive trait.
4.
F1: Wild type male crossed with a white eyed apterous female
F2: Resulting Eye Colors
Wild type male x mutant female
obs
exp
obsexp
(obsexp)2
/exp
red eyed females
385 186.25
198.75
39051.56
212
red eyed males
308 186.25
121.75
185.25
135.25
14823.06
79
34317.56
184
18292.56
98
white eyed females
white eyed males
total population: 745
degrees of freedom = 3
1 186.25
51 186.25
x2= 573
reject null
hypothesis
The chart above show a cross between a wild type male (XY) and a white eyed apterous
female (xx), and the resulting F2 generation phenotypes. This information can be seen in the
observed column for each phenotype. In order to perform a chi-squared analysis, the expected
values were calculated based on the understanding that all females should receive red eyes, since
they inherit the dominant copy from their father, and all males should receive white eyes, since
they only receive one recessive copy of the trait from their mother. This understanding comes
from crossing xx and XY in a Punnett square, using a 1:1:1:1 ratio, which was then scaled to the
total population of 745. The chi-squared test comes to be 573, resulting in a rejected null
hypothesis, with the null hypothesis being that the white eye mutant trait is an x-linked recessive
trait.
5.
F1: Wild type male crossed with a white eyed apterous female
F2: Resulting Eye Colors
Wild type male x mutant female
red eyes
white eyes
total population: 745
degrees of freedom= 1
obs
exp
obsexp
(obs-exp)2 /exp
693
558.75
134.25
18023.96
32.2
52
186.25
-134.25
18023.96
96.7
x2= 128.9
reject null
hypothesis
The chart above show a cross between a wild type male (XY) and a white eyed apterous
female (xx), and the resulting F2 generation phenotypes. This information can be seen in the
observed column for each phenotype. In order to perform a chi-squared analysis, the expected
values were calculated based on the understanding that all females should receive red eyes, since
they inherit the dominant copy from their father, and all males should receive white eyes, since
they only receive one recessive copy of the trait from their mother. This understanding comes
from crossing xx and XY in a Punnett square, using a 3:1 ratio, which was then scaled to the
total population of 745. The chi-squared test comes to be 128.9, resulting in a rejected null
hypothesis, with the null hypothesis being that the white eye mutant trait is an x-linked recessive
trait.
6.
F1: White-eyed apterous male crossed with a wild type female
F2: Resulting Eye Colors
White eyed apterous male x
normal female
red eyes
white eyes
total population: 256
degrees of freedom= 1
obs(obsobs
exp
exp
exp)2
/exp
152
192
-40
1600
8.3
104
64
40
1600
25
2
x = 33.3
reject null
hypothesis
The chart above show a cross between a White eyed apterous male (xY) and a wild type
female (Xx), and the resulting F2 generation phenotypes. This information can be seen in the
observed column for each phenotype. In order to perform a chi-squared analysis, the expected
values were calculated based on a 3:1 ratio created when crossing xY and Xx in a Punnett
square, which was then scaled to the total population of 256. The chi-squared test comes to be
33.3, resulting in a rejected null hypothesis, with the null hypothesis being that the white eye
mutant trait is an x-linked recessive trait.
7.
F1: White eyed apterous male crossed with wild type female
F2: Resulting Wing Type
White eyed apterous male x normal
female
normal wings
apterous wings
total population: 256
degrees of freedom= 1
obs
obsexp
exp
(obsexp)2
/exp
238
192
46
2116
11
18
64
-46
2116
33
x2= 44.0
reject null
hypothesis
The chart above show a cross between a wild type female (Ww) and a white eyed
apterous male (ww), and the resulting F2 generation phenotypes. This information can be seen in
the observed column for each phenotype. In order to perform a chi-squared analysis, the
expected values were calculated based on a 3:1 ratio created when crossing ww and Ww in a
Punnett square, which was then scaled to the total population of 256. The chi-squared test comes
to be 44.0, resulting in a rejected null hypothesis, with the null hypothesis being that the apterous
wing mutant trait is an autosomal recessive trait.
8.
F1: Wild type male crossed with a white eyed apterous female
F2: Resulting Wing Type
Wild type male x mutant female
normal wings
apterous wings
total population: 745
degrees of freedom= 1
obs
exp
714 558.75
31 186.25
obsexp
(obsexp)2
155.25
155.25
24102.56
43.1
24102.56
129.4
/exp
x2= 172.5
reject null
hypothesis
The chart above show a cross between a wild type male (Ww) and a white eyed apterous
female (ww), and the resulting F2 generation phenotypes. This information can be seen in the
observed column for each phenotype. In order to perform a chi-squared analysis, the expected
values were calculated based on a 3:1 ratio created when crossing ww and Ww in a Punnett
square, which was then scaled to the total population of 745. The chi-squared test comes to be
172.5, resulting in a rejected null hypothesis, with the null hypothesis being that the apterous
wing mutant trait is an autosomal recessive trait.
Discussion: The data gathered does not support the hypothesis. When crossing the Po
generation, the resulting F1 phenotypes does coincide with what is to be expected based on the
hypothesis; however, when moving forward with the experiment and crossing a F1 generation to
create a F2 generation, the data collected does not support the hypothesis. With the knowledge
that the Po generation is homozygous for both the wild-type mother and mutant father, and with
the hypothesis being that white eye color is a recessive x-linked trait and apterous wings are a
recessive autosomal trait, the F1 phenotypes are expected to be all red-eyed and normal-winged,
for both males and females. In this instance, the data certainly verifies the hypothesis. The
experiment then moves forward as the normal females and the normal males from the F1
generation, which are now heterozygotes, are mixed with their mutant counterparts. This is when
the data gathered by the experiment does not necessarily coincide with what was to be expected
based on the original hypothesis. When mixing a normal heterozygous female with a mutant
homozygous male, according to the hypothesis that the white eye color is x-linked recessive and
the apterous wing is autosomal recessive, the resulting F2 generation should be comprised of
three fourths normal, and one fourths mutant. This did not happen, and the chi square test points
to rejecting the hypothesis for that reason. The same scenario appears when crossing a normal
heterozygous male with a mutant homozygous female. The resulting F2 generation should be
comprised of three fourths red-eyed and one fourths white-eyed, and three fourth normal wings
and one fourth apterous winged. Again, this did not happen, and the chi square test exhibits that
through rejecting the original hypothesis. This experiment then would lead to inconclusive
results, as the Po cross to F1 generation resulted in data supporting the hypothesis, while the F1
cross to F2 generation resulted in data that did not support the hypothesis. While the results
prove to be inconclusive, scientific precedence says otherwise. It is an understood fact that eye
color is an x-linked, and that the mutant white eye color is recessive; it is also an understood fact
that wing type is an autosomal trait, and that the mutant apterous wing type is recessive (R.
Piergentili 2010). This being said, for the experiment to result in the way it did, there is room for
only two explanations, human error and limitations on the chi-square data due to too small of
numbers. The experimenters must have incorrectly accounted for the number of each phenotype
in the F2 generation; this can be attributed to a number of factors such as lack of time, large
amounts of flies to work with, etc. The phenotypes in the F2 generation should have been
distributed the way they were expected to solely based on a scientific consensus that’s been
understood for many years; the only logical reason that they weren’t has to be because of human
error. While the experiment yielded inconclusive results, based on scientific principle, the
original hypothesis, which states that the mutant white eye color is x-linked recessive and the
mutant apterous wing type is autosomal recessive, with each of these trait’s mode of inheritance
being recessive, has to be correct even though the experiment is not indicative of that.
Literature Cited
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Nature.com. Nature Publishing Group, n.d. Web. 08 Oct. 2014.
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(2012):
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<http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3454882/>.
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