A Study Of Inheritable Traits In Fruit Flies

A Study Of Inheritable Traits in Fruit Flies

INTRODUCTION

The Drosophila melanogaster, more commonly known as the fruit fly, is a

popular species used in genetic experiments. In fact, Thomas Hunt Morgan began

using Drosophila in the early 1900’s to study genes and their relation to

certain chromosomes(Biology 263). Scientists have located over 500 genes on the

four chromosomes in the fly. There are many advantages in using Drosophila for

these types of studies. Drosophila melanogaster can lay hundreds of eggs after

just one mating, and have a generation time of two weeks at 21°C(Genetics:

Drosophila Crosses 9). Another reason for using fruit flies is that they mature

rather quickly and don’t require very much space. Drosophila melanogaster has a

life cycle of four specific stages. The first stage is the egg, which is about .

5mm long. In the 24 hours when the fly is in the egg stage, numerous cleavage

nuclei form. Next, the egg hatches to reveal the larva. During this stage,

growth and molting occur. Once growth is complete, the Drosophila enter the

pupal stage, where it develops into an adult through metamorphosis. Upon

reaching adulthood, the flies are ready to mate and produce the next generation

of Drosophila melanogaster.

During this experiment, monohybrid and dihybrid crosses were conducted

with Drosophila melanogaster. Our objective was to examine the inheritance from

one generation to the next. We collected the data from the crosses and analyzed

them in relation to the expected results.

MATERIALS AND METHODS

For the monohybrid cross in this experiment, we used an F1 generation, which

resulted from the mating of a male homozygous wild-type eyed fly with a female

homozygous sepia eyed fly. Males and females are distinguished by differences in

body shape and size. Males have a darker and rounder abdomen in comparison to

females, which are more pointed. Another difference occurs on the forelegs of

the flies—males have a small bump called sex combs. At week 0, after being

anaesthitized by fly-nap, three males and three females were identified under a

dissecting microscope and placed in a plastic vial with a foam stopper at the

end. The vial remained on it’s side until the flies regained consciousness so

that they didn’t get trapped by the culture medium at the bottom. We allowed

the Drosophila to incub...

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...eighed the number of males. This may imply that the X chromosome

is dominant over the Y chromosome. This would cause the X chromosome to mix

with another X chromosome, producing a female, more often than it would mix with

the Y chromosome, which would produce a male. As a follow-up to the experiment,

I would perform many more trials than each person did for this experiment. Also,

more flies could be placed in each vial to ensure even more offspring to be

included in the data. I would also be sure to remove the flies after just one

week to reduce breeding between generations. This experiment caused Mendel’s

findings to be more concrete and realistic in my mind. It made the information

more than meaningless numbers. The experiment also made me realize how easily

biological ideas can be proved. Our results agree with Mendel’s discoveries.

The only drawback to our learning was the massacre of over 26,000 fruit flies.

REFERENCES

Campbell, Neil A., Biology: Fourth Edition. Menlo Park: Benjamin/Cummings,

1996.

"Genetics: Drosophila Crosses." Lab Handouts, General Biology Lab, 2008.

"So What’s a Monohybrid Cross Anyway?" Lab Handouts, General Biology Lab, 2008.