Throughout we were required to record the numbers

Throughout this
experiment we were able to investigate and learn the basic principles of
monohybrid inheritance by observing Drosophila. Throughput our observations we
were required to record the numbers of flies that displayed mutant traits. We
then were able to observe the way mutant traits are passed down from one
generation to the next. With the data we collected, we were then able to
construct a hypothesis to describe the mode of inheritance for a mutation.

Introduction

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Drosophila melanogaster,
also known as the fruit fly is one of the most commonly used and understood
model organisms. Why use Drosophila? There are many different things that make
Drosophila so valuable for the study of genetics and development, some of these
include: inexpensive, short reproductive cycle, easy maintenance and storage,
full genome was decoded and published in the year of 2000. The fly’s life cycle
is completed within about 12 days. One main difference between males and
females are the shape and color of the posterior abdomen. Males will have
darker and wider posteriors than the females. Another difference is that male
flies have a sex combs on their upper forelegs while females don’t.

What is dominance and
recessiveness? Dominant alleles are shown whenever the individual has one copy
of the dominant allele. (Heterozygous) Recessive alleles are shown whenever the
individual has two copies of the same recessive allele. (Homozygous) There is
also a possibility for both alleles to be dominant, each for a different trait,
resulting in both alleles being shown equally as much. This is known as
codominance.

A monohybrid cross is the
mating between two different individuals that have different alleles at one
specific locus. Chi-square analysis is a statistical analysis that is used to
determine whether you should accept or reject your null hypothesis. Accept the
null hypothesis when the deviation can be attributed to chance alone. Reject
the null hypothesis when the deviation is unable to be attributed to chance
alone.

The purpose of this
experiment is to learn about the basic principles of monohybrid inheritance. I
expected that the experiment would show a 3:1 phenotypic ratio. I expected this
because of Mendel’s research of a monohybrid cross that showed a 3:1 phenotypic
ratio.

In the experiment we used
two different types of Drosophila, wild type flies (winged) and mutant apterous
flies. (wingless)

Materials

·        
One vial of wild-type Drosophila (winged)

·        
One vial of mutant apterous Drosophila
(wingless)

·        
Sorting brushes

·        
Microscope

·        
Notecards

·        
FlyNap

 

 

 

 

Methods

Week
1

Part
1: Observed and Sexed Drosophila

During week 1 we received
two different vials, P1 and P2. One vial contained
wild-type Drosophila and the other contained mutant type apterous flies. We then
practiced the procedure for administering the FlyNap to the flies. This was
important for ensuring that our flies wouldn’t die from an overuse of the
FlyNap. Once we were comfortable with the procedure we then used the FlyNap on
each vial of flies. We then knocked placed them on notecards and under a
microscope for observation. Comparing the mutants with the wild-type flies. We
also sexed the flies. Recording the sex and phenotypes.

Part
2: Setting up F1 vials

We then received an empty
vial that we labeled with our group name and description of the cross labeled F1.
We moved the anesthetized P1 and P2 flies, including
males of one phenotype and virgin females for the other into this new F1
vial.

Week
2

Part
3: Clearing of F1 vials

Approximately a week
later after the cross has started, we were instructed to remove the parents
from the F1 vial using FlyNap and transfer them into the morgue.
This was imperative to ensure there wasn’t any genetic crossover between the
parents and the F1 generation.

Week
3

Part
4: Setting up F2 vials

During week 3 we were
instructed to use FlyNap on the flies and place them onto a notecard for
observation. We then used brushes to sort and identify the flies phenotype.
While also scoring the flies, including the number of males and females that
display wild-type and mutant apterous phenotype. Then we divided an equal
number of males and females from the F1 vial into a new vial labeled
with our group’s name and F2.

Week
4

Part
5: Clearing F2 vials

During week 5, we were
instructed to remove the F1 adult flies that were previously
transferred into the F2 vials using FlyNap to prevent any type of
generational crossover. We then disposed of these flies into the morgue.

Week
5

Checked on our flies.

Week
6

Part
6: Scoring F2 Flies

Approximately 10-14 days
later we were instructed to anesthize the F2 vials using FlyNap and
place them onto a notecard. We then observed the flies underneath the
microscope and sorted them with brushes to score and identify the phenotypes.
Recording the number of males and females that display wild-type and mutant
apterous phenotype.

 

Results and Discussion

The P1 Generation
consisted of a monohybrid cross between wild type and mutant apterous resulting
in the F1 generation displaying all wild type.

 

 

 

 

 

 

 

The results for the cross
between the first and second-generation mating had displayed a 3:1 phenotypic
ratio. ¾ of the individuals were wild-type and ¼ were apterous. This is because
wild-type phenotype is dominant over the apterous phenotype. We used the method
of true breeding. This is when an individual is homozygous for every trait for
the P1 generation. Which resulted in a phenotype of 100% wild-type.
Concluding that the F1 generation was heterozygous, containing both
a dominant and recessive allele.

 

 

 

 

 

 

 

Regarding the results
from Chi-square analysis, we were able to accept the null hypothesis for both
the F2 vials. (top left/bottom left) This means that the deviations
can be attributed to chance alone. We were also able to accept the null
hypothesis for the F2 vial (top right) and reject the null
hypothesis for the F2 vial. (bottom right) By rejecting the null
hypothesis we are admitting that the deviation can not be attributed to chance
alone.

Throughout our experiment
we learned about the basic principles of monohybrid inheritance. We crossed
both a wild-type Drosophila with an Apterous Drosophila to explore the way a
mutant trait is passed down from one generation to the next. The results for
the P1 generation had went as I had expected. When a dominant
wildtype Drosophila (AA) is crossed with a mutant apterous Drosophila (aa), a
3:1 ratio is expected. ¾ being wildtype and ¼ being apterous for the F1
generation.

Regarding the results
from Chi-square analysis, we were able to accept the null hypothesis for both
the F2 vials. (top left/bottom left) This means that the deviations
can be attributed to chance alone. We were also able to accept the null
hypothesis for the F2 vial (top right) and reject the null
hypothesis for the F2 vial. (bottom right) By rejecting the null
hypothesis we are admitting that the deviation cannot be attributed to chance
alone. The reason for rejecting the null hypothesis could have been the result
of a miscalculation or observation of the Drosophila’s phenotypes. One
difficulty throughout this experiment was keeping the flies from falling into
their food and getting stuck after anesthizing them with the FlyNap. Another
difficulty is that the food would also occasionally fall out of the vial along
with the flies. I enjoyed being able to observe the way mutations are passed
down from one generation to the next.

Precautions

1)     
When using the FlyNap to anesthetize the
flies, make sure to tilt the vial on its side. This will help to prevent any
flies from falling into the food.

2)     
Be careful not to use too much FlyNap to
anesthetize the flies. This may result in the death of the flies.

3)     
When clearing the vials of the adult flies
be sure to get all of them, if not it will result in generational crossover.

4)     
When dealing with the vials there are many
flies so be sure to avoid any scoring errors and escaping flies.

References

Education, P. (2017). Modified
Mastering Genetics with Pearson eText — Standalone Access Card — for
Essentials of Genetics, 9th Edition