I never got to participate in a science fair when I was in school. We simply didn't have any available. Now, there are a number of opportunities, including the Central Interior Science Exhibition this week.
However, if I had been able to enter a science fair, I think that I would have done an experiment on fruit fly genetics.
That might sound a little strange because I am now a chemist. However, studying fruit fly genetics was an experiment that we did in Grade 8 Biology. I found it fascinating that we could do genetic analysis with such a simple experiment.
I also became very proficient at drawing fruit flies.
It wasn't until many years later that I learned about the extensive research done by leading scientists on fruit flies or drosophila melanogaster to use their proper name. We owe the annoying little flies a debt of gratitude for their role in uncovering the machinery of the cell.
Charles W. Woodworth is often credited with being the first to suggest the use of fruit flies in genetic experiments. However, it was in Thomas Morgan's lab that studies in fruit flies really took off. He won a Nobel Prize for his work.
In many ways, fruit flies are the ideal species to study. They don't eat much and can live on many different types of food. They don't take up much space. Most of the early experiments were done by breeding the flies in milk bottles. Indeed, rumour has it that many a milkman found the empty bottles missing during his rounds.
Fruit fly males and females are easy to tell apart and it is easy to separate virgin females which allows for control of breeding. The females lay a large number of eggs resulting in a large number of offspring which helps with the statistical analysis of traits.
But perhaps the most important characteristic is that fruit flies have a very short generational interlude. From birth to reproduction is typically 10 days at room temperature. That affords a curious scientist three generations of flies per month and 36 generations per year.
Generations are important in studying genetics. A gene controls the production of proteins within an individual cell. Indeed, it was once a major axiom of biology that one gene equals one protein. We now know that things are a little more complicated.
However, in the early 1900s, when Morgan and his group were first carrying out experiments in genetics, no one even knew what genes were or where they were located. All biologists had to go on was the expression of a gene in the organism. How a particular trait was expressed from one generation to the next was critically important.
Under average circumstances, you get an average fruit fly. It looks like all other fruit flies with large, bulbous red eyes and a striped body. This doesn't really tell you much about the fruit fly's genetics.
Every now and then when breeding fruit flies a mutant emerges. For example, white eyes are reasonably common. When you get a fly with white eyes, you can know that something has changed. The fly's genes are not the same.
Careful breeding of white eyed flies with other flies and examining the resulting off-spring tells you something about how the genetic information is transmitted from one generation to the next. That, in turns, tells you something about the genes of the fruit fly.
By analyzing generation after generation of fruit fly, Morgan and his co-workers were able to learn a great deal about the genetics of fruit flies. For example, when a white eyed male was bred with a red eyed female, the resulting off spring all have red eyes.
But in the next generation, the white eyed trait re-emerges which is the pattern that is expected for a recessive trait. More importantly, they found that all of the white eyed off-spring were male which means that the trait is sex-linked and must occur on the sex chromosome.
Indeed, it was through working with fruit flies that they came to realize that the genetic material could be found on the chromosomes.
Morgan and his group were also able to show that some traits are linked but occasionally the linkage would break down.
In a brilliant moment of insight, it was realized that this was a measure of how far apart the genes were from one another on a chromosome. The further apart, the more likely it would be for two genes to uncouple. We now know that the chromosomes sometimes exchange genes.
Careful mapping of all of the mutations in fruit flies eventually led to the first complete map of the organisms chromosomes.
So, working on fruit fly genetics is another step in the long history of genetics. That would have made a good science fair experiment.
