Thomas Hunt Morgan's Fruit Fly Experiment

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  • 0:00 Morgan's Fruit Fly Experiment
  • 1:02 The Experiment
  • 2:04 Significance of the Experiment
  • 4:54 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

In 1910, American scientist Thomas Hunt Morgan conducted an experiment with a bunch of flies that changed our understanding of genetics. In this lesson, we'll look at Morgan's famous experiment and discover how it defined modern genetics.

Morgan's Fruit Fly Experiment

Do you ever wish you could go back and see some of the great moments in history? Well, great news, you can! This is a time machine. Yes, it works - but only for about six minutes and only within the confines of your computer screen. So, what do you want to see? The invention of the wheel? The discovery of bacon? Can you imagine the look on that guy's face? Oh, I know - how about the founding of experimental genetics, the field of research that studies the ways that DNA and genes are passed, mutated, and maintained by breeding test subjects for certain traits? To see the origins of this field, we're heading back to 1910, to see the fruit fly experiment in which Thomas Hunt Morgan confirmed that genes are located on chromosomes and discovered the relationship between dominant and recessive traits. How did he do this with a bunch of flies? Well, hop on in, and let's take a trip back through history.

The Experiment

Here we are in back in 1910, and there's Thomas Hunt Morgan right there. For the last few years, he has been researching drosophila melanogaster, the common fruit fly, looking for mutations that could show how species evolve. Fruit flies make great research subjects because they mature and reproduce quickly, so you can observe changes over several generations in a matter of days. After breeding literally millions of flies, Morgan discovered a single fly that had developed white eyes, as opposed to the normal red eyes. Morgan bred this white-eyed fly with an ordinary red-eyed fly and waited to see what happened.

In the first generation of offspring from that group, only three of the 1,200 flies had white eyes. However, by the second generation, a much larger number of white-eyed flies appeared. Even more surprisingly, every single one of the white-eyed flies was male.

Significance of the Experiment

Some flies have red eyes, and some have white eyes. So what? Well, through this experiment, Morgan had unwittingly proven that some early theories on genetics, theories he himself were skeptical of, were in fact accurate. First, by showing that the trait of white eyes could be passed on from generation to generation, Morgan demonstrated that such traits were carried on genes, which was still a relatively new idea at this time - so much so, in fact, that the actual term 'gene' wouldn't be coined for a few more years.

Even more significantly though, the higher number of flies with white eyes in the second generation showed that these traits could be passed on even through flies that did not display them. What this confirmed was the Mendelian theory of inheritance, first proposed by Gregor Mendel in 1866. According to this theory, traits can be either dominant or recessive, and for recessive traits to become visible, the offspring must have received a recessive gene from each parent but no dominant gene for that trait. In the fruit fly experiment, this meant that about half of the fruit flies in the first generation had the recessive white-eye trait within their DNA, even if the actual eye color was red, the dominant trait. Then, this recessive trait was passed on to the next generation, demonstrating that recessive traits are passed on, even if they are not visible in the parent. This was huge for genetics research. The ideas about dominant and recessive traits were out there but not confirmed in the 20th century until now.

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