Induction of Mutation in Drosophila melanogaster

Submitted by Group 8

Salumbre, RenzSalvador, Meliza Ylaine

Sobrevega, Paul ChristianSurquia, Joseph Michael

Submitted to

Ms. Gardette ValmonteMr. Francis Abrantes

October 11, 2007

INTRODUCTION

Drosophila melanogaster, commonly known as fruit flies, are said to be the

perfect organisms for investigating the principles of experimental genetics. There are

many reasons why is it so, however some of the most common are 1) the convenience of

culturing the said organisms; 2) it has a short generation span and that females can

approximately lay 700 eggs in a single day; 3) mature larvae exhibit polytene

chromosomes indicative of the process of transcription and other gene activity; 4) its

inherent quality in that it contains only three autosomes and one sex chromosome.

In this experiment, formaldehyde was used as an inducer of mutation. It is the

simplest member of the aldehyde family with the formula CH2O and is usually employed

as a disinfectant and a preserving solution. Its typical characteristics are its pungent

smell, flammability and solubility in water.

Frequency of mutation in the fruit flies has been well documented. Mutation, as

an event that gives rise to heritable alteration in the genotype, in the fruit flies may be

classified as dominant or recessive; visible, lethal or biochemical. Visible mutations are

essentially identified as the loss of a function or a structure resulting in an observed

difference in the morphology of the organism. Lethal mutations, however, are the ones

that cause immediate death of the organism since the mutation has occurred during

embryonic development. Lethal mutations are also known as chromosomal aberrations or

mutations. Lastly, biochemical mutations are usually connected in relation to the

organism’s enzymatic reactions. It may mean as the loss of ability to synthesize an

essential metabolite. Biochemical mutations underlie the principles of visible and lethal

mutations.

In this experiment, the objectives were to induce mutation using formaldehyde

and to compare the degree of mutation in three different concentrations of formaldehyde.

MATERIALS AND METHOD

In the experiment, the materials that were utilized were the following: four

sterilized culture bottles; strips of filter paper; ripe saba; yeast; propanoic acid; cotton

plugs; formaldehyde and the fruit flies.

The methodology first consisted of preparing the culture bottles. Ripe saba

bananas were mashed and divided into four equal parts (corresponding to the four culture

bottles). Then the preparation of formaldehyde was performed by deriving the

concentrations of formaldehyde in each bottle using the formula C1V1 = C2V2. The

different concentrations were then applied to the four culture bottles and labeled as 0%,

0.1%, 0.2% and 0.3%. Five pairs of fruit flies were inserted in each bottle and considered

as initial parental generation or P0 generation. The fruit flies were then allowed to

reproduce until the first filial generation and the progeny of P0 etherized using

chloroform. Observation of mutations was done using a dissecting microscope or a

magnifying glass.

RESULTS AND DISCUSSION

To reiterate, mutation is a random change in a gene or chromosome resulting into

a new trait or characteristic that can be inherited. It can be a source of beneficial genetic

variation or it can be neutral or harmful in effect. Furthermore, mutation can be obtained

either by inducement or just by spontaneous occurrence. The former is caused by

intentional addition or exposure of mutagens, such as UV rays, x-ray radiation and

chemicals that can react with the DNA of an organism. On the other hand, the latter,

refers to DNA damage that results from naturally occurring alterations within the genetic

information. These are deletions and insertions, which can give rise to certain damages to

the whole organism.

In the experiment, an induced mutation was applied by simply exposing the fruit

flies into four different concentrations of formaldehyde, namely 0%

(controlled), .1%, .2% and .3%. The volume of formaldehyde to be added was calculated

in accordance to the volume of the medium (saba) to be used using the C1V1=C2V2

formula, to obtain the right ratio of the two substances to be mixed.

Based on the fruit flies that have been gathered, 3 major observations can be

obtained. First, there is a relatively low number of population of flies in the experimental

bottles compared with the control. It can be deduced that for every 5 adult flies being

developed in the control bottle only 1 fly is grown to its adult stage from the experimental

bottles, giving a 5:1 ratio. Second, in relation with the first, the growth of the flies tend to

linger most of its time at its pupa stage, having a reduced number of adult flies. Lastly,

some of its pupa shows a different color with the normal ones and as well as most of the

abdominal tips of the adult flies where filled with black pigment.

Even though the protocols of the experiment did not require the determination of

mutation by handling directly its gene sequence, it can be inferred that there was a

minimal percentage of mutation that had happened. This is because, in spite the fact, that

formaldehyde was known as a preservative, insecticide, and deodorant, still flies are able

to produce and perpetuate. But its growth is in a modified manner, which is base on the

adaptive mechanism that they are able to acquire as a response to the environment that

they were forcibly exposed into. Moreover, within the chemical structure of

formaldehyde, it was known that it can hydrolyze proteins, therefore a change with that

certain function of protein within the flies’ DNA can lead to the process of producing

genetic aberrations, that can be lethal. Furthermore, its lethality can either be based on its

gender or just by its dominance or recessiveness regardless of its gender that may have

affected the number of our progenies. Consequently, this will all be surely expressed unto

its phenotypic characteristics, covering both of its growth and development.

REFERENCES

Cook, H. Molecular characterization of an unknown P-element insertion in

Drosophila melanogaster. Laboratory Manual, 2005.

Levine, R.P. Genetics. Holt, Rinehart and Winston, Inc. : USA, 1962

Strickberger, M.W. Experiments in Genetics with Drosophila. John Wiley and Sons:

New York , 1962.