Fruit Fly Internet Research
schmied/reid©2000
Drosophila melanogaster Name __________
aka The Infamous Fruit Fly Period ____
Student #___
(OK &endash; this might be considered to be a little bit thick for an average seventh grader, but then again you aren't average! Get what you can from it and ask questions about things you don't understand!) What is Drosophila? - Drosophila melanogaster is the scientific name for the common Fruit fly. Drosophila has been used as a model organism for research for over a century and has been one of the most valuable organisms ever used in genetics and developmental biological research.
Why do scientists work with Drosophila? Well, people study Drosophila for two reasons:
„ First - many aspects of its biology are well understood. This knowledge allows scientists to study very specific questions about the Fruit fly easily.
„ Second, Fruit flies are small animals, with a short life cycle (just two weeks), so it is cheap and easy to keep large numbers of Fruit flies... and the results come fast (in two weeks)!
„ In addition, many Mutant flies, with defects in any of several thousand genes are available for comparison studies. So, using Drosophila as a study subject has many benefits, in knowledge, time, and cost.
So what does all this research mean for me and you? It has been discovered that Fruit flies have genes on their chromosomes (genetic material) that are identical to those in humans!! Why is this important? Its important because genes tell your cells to make different proteins.... and these proteins make your body do stuff.... and if we can find out what these identical proteins do in Fruit flies, we can get an idea what they do in us!!! (OK, we can't use the knowledge to sprout wings, but we can use it to tell us all kinds of other neat stuff like what happens when a single protein is made incorrectly. (a mutation)
Life cycle of Drosophila - Drosophila has a four stage life cycle in which it undergoes metamorphosis. At a temperature of 21ūC *, Drosophila melanogaster will produce new adults in two weeks; eight days in the egg and larval stages, and six days in the pupa stage. The life span of a fruit fly may be several weeks. (* Fruit flies are cold blooded, so metamorphosis takes longer in cold conditions.)
„ Egg: The whitish Drosophila egg is about half a millimeter long. It takes about one day after fertilization for the embryo to develop and hatch into a worm-like larva.
„ Larva - The voracious larva (sometimes called a maggot!) eats and grows continuously, moulting one day, two days, and four days after hatching (the larva stages are called first, second and third instars). The pupa develops from the third instar which becomes hard in texture and dark in color.
„ Pupa - In an amazing feat of acrobatic rearrangement, the larva's body is completely remodeled (metamorphosed) inside the pupa case in just four days to give the adult winged form! The pupa darkens just before the adult emerges. If you look closely through the pupa a day before the adult emerges you can see the folded wings and the pigment of the eyes
„ Adult - the adult forces its way through the operculum at the anterior, or the head, end of the pupa. At first the fruit fly appears light in color with a long abdomen and folded wings. Within a few hours the fly gets darker in color, rounder in the abdomen and pumps its wings out to the extended position. Adult fruit flies are small (about 3mm in length), light colored. and have brilliant red eyes. They have black lines around their abdomen, clear wings, and have a humpbacked appearance when viewed closely.
„ Mating - The males are the smaller of the two sexes. They have black, rounded abdomens, while females have a banded, pointed abdomen. There are only 12 hours that a female can be considered virgin after emerging as an adult. About 48 hours after emerging from the pupa, it is possible for females to start laying eggs. (At 25ūC the adults become fertile in just one day, but development takes twice as long at 18°C.) After reaching this maturity, the flies are fertile for life. A female fruit fly can store sperm after a single insemination and use it for many reproductions, That's why it is important to use virgin females for genetic crosses.
„ Biology Female fruit flies lay about 500 eggs near exposed fruit, juices or fermenting substances. Larvae hatch in a day and feed on organic substances. Larva pupate in an isolated area. The life cycle is complete in about 2 weeks. Since fruit flies have a very high fecundity rate, they are considered to be a major pest species.
Fruit flies are a problem around breweries, restaurants and fruit warehouses. Most commonly found around exposed garbage cans, they will feed on juices and exposed rotting fruit. Fruit flies are sometimes termed "vinegar flies" at times for their habit of collecting around mops and rags used for cleaning operations. They were once commonly called Pomace flies.
Historical research on Drosophila - (A genome is considered the entire set of genetic blueprints of an organism. These blueprints determine how the organism will look and how it will function chemically.)
Scientists have made some of their greatest genetic discoveries while studying Drosophila! For example, when observing the four pairs of chromosomes each fruit fly has, scientists noticed that males had one pair of homologous chromosomes that were not the same size, while all pairs were the same size in females. This odd sized chromosome was linked to determining the sex of the flies. (and human males too!)
Discoveries that males were more likely to inherit certain recessive (hidden) traits led to the foundation of a sex linked trait theory. Other linked traits were found and irregularities in linked traits led to the discovery of mutations caused by crossing over chromosomes. Also, when a fruit fly larva grows, it keeps the same amount of cells in its salivary glands but makes hundreds of copies of its DNA in preparation for the pupa stage. These copied chromosomes stay together, making an enormous chromosome with repetitive bands on it. By observing these bands they began to make a map of all the genes on the Drosophila chromosomes.
It is now estimated that Drosophila has a genome of about 165 million bases and contains and estimated 12,000 genes (by comparison, the human genome has 3,300 million bases and may have about 70,000 genes; yeast has about 5800 genes in 13.5 million base bases).
Though declining in use, Drosophila are useful in genetic experiments to study basic genetic principles. Today they are mainly used in developmental studies. For example to discover how a developing cell knows how to become a leg or wing. In any event, without fruit fly studies, many of the truths of genetics that we take for granted may never have been discovered!
Enrichment information When genetics was first studied in Gregor Mendel's experiments, pea plants were used to observe how traits were passed down generations. Through these experiments he developed three laws: the basis of genetics today.
First is the principle of dominance, which states that one factor, or gene, in a pair may prevent the other from showing up.
The second , the principle of segregation, says that like traits separatewhen gametes are formed. This is important because if they did not separate organisms would become big blobs of genetic material.
The third principle, independent assortment, says that each chromosome pair divides independently. If this principle were not true then there would only be two different trait combinations in a species instead of billions.
Even though the pea plants Mendel produced useful genetic truths, one had to wait to identify offspring traits because of the lengthy maturation period. To shorten the wait, geneticists began to use a species of fruit fly called Drosophila melanogaster, commonly called the red-eyed pomace fly. This species has only a fourteen day life cycle, and reproduce quickly to keep their species alive. "The egg, a mere half millimeter long, hatches one day after fertilization into a larva. This worm-like creature molts three times within four days and two days later it hardens into a stationary pupa. Just like caterpillars, these pupa completely transform into adults over a period of four days. The adult fly then breaks out of its casing, develops quickly over the next 24 hours, and becomes a fertile adult. It lives for about seven more days, breeding often. Such speedy maturity and lengthy fertile time creates at least three generations in a matter of weeks. These flies are small and only require little food and living space, so hundreds can be kept in a single vial without overcrowding. With only three pairs of autosomes and one pair of sex chromosomes, much fewer than peas, it is easier to trace traits to specific chromosomes. These and other pros led to the universal use of Drosophila as a laboratory species for genetic experiments.
Drosophila has four pairs of chromosomes: the X/Y sex chromosomes and the autosomes 2,3, and 4. The fourth chromosome is quite tiny and rarely heard from. The size of the genome is about 165 million bases and contains and estimated 12,000 genes (by comparison, the human genome has 3,300 million bases and may have about 70,000 genes; yeast has about 5800 genes in 13.5 million base bases). There is now a major effort underway to map and sequence the entire Drosophila genome.
Polytene Chromosomes (huge chromosome that are easy to study due to their large size!) These are the magic markers that first put Drosophila in the spotlight. As the fly larva grows, it keeps the same number of cells, but needs to make much more gene product. The result is that the cells get much bigger and each chromosome divides hundreds of times, but all the strands stay attached to each other. The result is a massively thick polytene chromosome, which can easily be seen under the microscope.
Even better, these chromosomes have a pattern of dark and light bands, like a bar code, which is unique for each section of the chromosome. As a result, by reading the polytene bands, you can see what part of the chromosome you are looking at. Any large deletions, or other rearrangements of part of a chromosome can be identified, and using modern nucleic acid probes, individual cloned genes can be placed on the polytene map!
Finding out more about Drosophila melanogaster.....
Online
Descriptive (note these references came from the scientific site above.)
Many biology and developmental biology textbooks have chapters on Drosophila. There are fewer books devoted specifically to Drosophila; here are a some:
The Making of a Fly (Peter Lawrence; Blackwell Scientific, 1992).
This is probably the easiest simple introduction to Drosophila development and quite readable.
Drosophila (Brian Shorrocks; Ginn & Co, London, 1972)
An interesting slim volume looking at the general biology of the fly, with chapters on laboratory and field ecology, simple genetics, behavior and techniques, from a zoological perspective.
Probably out of print, but should be in many academic libraries.
The Development of Drosophila melanogaster (ed. Bate & Martinez-Arias; Cold Spring Harbor Press, 1993)
Biology of Drosophila (ed. M. Demerec; Cold Spring Harbor Press, 1994).
This reprint of the classic 'Demerec' book of 1950 covers a great deal of descriptive biology of the fly, and is available for about USD$40, quite a bargain for an academic book.
Techniques
Drosophila, a Practical Approach (ed. DB Roberts; IRL Press, 1986).
Edited book covering such techniques as lab culture, molecular biology and mutagenesis.
Drosophila, a Laboratory Manual (Michael Ashburner; Cold Spring Harbor Press, 1989)
Recipe book for many techniques, ranging from the popular to the obscure.
Video
The Lives of a Fly by Mary Tyler is a VHS video which gives a general introduction to fly development.
Insect control
Bennett: Scientific Guide to Pest Control Operations
Christensen, Chris. Technician's handbook to the Indentification and Control of Insect Pests
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©2000 John Schmied and Mike Reid