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Thomas Hunt Morgan Biography

Instructor: Jeremy Battista
Without the countless efforts by scientists over the years, we would know little to nothing about our world. Thomas Hunt Morgan's experiments with genes, chromosomes, and inheritance gave further proof of how we get the features that we get.

Early Life

Thomas Hunt Morgan

Thomas Hunt Morgan was born in 1866 in Lexington, KY. He was born to a more or less 'elite' family that had connections to the Confederacy during the Civil War. Through his mother, he was the great-grandson of Francis Scott Key, of The Star Spangled Banner fame.

By 1886 he had graduated as valedictorian from what would become the University of Kentucky. He majored in science, working with the U.S. Geological Survey during his summers, and he also studied marine biology. Morgan moved on to Johns Hopkins University where he earned a master's degree. Shortly thereafter he received a fellowship and worked on his research at Johns Hopkins University.

He eventually became an associate professor at Bryn Mawr College in Pennsylvania, before moving on to Columbia University. It is here where he began his work that would emblazon him in the minds of scientists for ages to come.

Experiments

As stated earlier, Morgan's contributions to science focused around inheritance of genes, similar to Gregor Mendel's experiments. At first, Morgan was skeptical about Gregor Mendel's conclusions about inheritance. He set out to create his own experiments and draw his own conclusions.

Instead of pea plants, Morgan instead chose to study Drosophila melanogaster, a specific species of fruit fly. He chose the fruit fly because as anyone who has ever had fruit flies knows, they breed and produce hundreds of offspring in one shot. More offspring equals more experimental results.

Another reason for the use of these fruit flies is that they only have four chromosomes (DNA) that can be seen with a simple light microscope rather than a huge electron microscope. He worked for a year to breed and cross these fruit flies with one another, something that would have been a little strange at that time. After a year, he found a strange occurrence: instead of all the flies having dominant red eyes (known as the wild type), he found flies with white eyes (recessive).

Morgan took his white-eyed male fly and mated it with a red-eyed female fly. The results were what one would expect from a cross such as this: all offspring ended up red-eyed, which is the dominant trait. He then went ahead and bred this generation of offspring amongst themselves and again, similar to Mendel's pea plants, found that the ratio of red-eyed flies to white-eyed flies was three to one. What Morgan also found was something that Mendel had not seen with his plants. Thomas Morgan discovered that only the male flies ended up with white eyes. He had no females with white eyes.

He started trying to figure out what could be the cause of this and eventually determined that the eye color was directly correlated with their sex chromosomes. Similar to humans, flies have XX chromosomes for females and XY chromosomes for males. The white eye color, he deduced, must have been linked to the sex chromosomes. There was no place for the eye color on the Y chromosome so the key was the X chromosome.

The white eye color is recessive, so for the females to get white eyes, they would need a copy of the allele (variety of a gene) on each X chromosome. For the second generation he had bred, that was impossible to occur. The males on the other hand, only need one copy of the allele because they only have one X chromosome. The further the generations went on, the more opportunity there was for the females to have white eyes.

Morgan also ran experiments on wings and body types. Without getting into many of the specifics, he was able to find similar results to his eye color crosses. The only difference here was that the different genes for body color and wing type were actually linked. He was able to discover linked genes which are similar in scope to sex-linked genes, but these genes were linked to one another rather than to the sex chromosomes. Morgan was able to reason that body color and wing type are actually inherited together rather than separate.

Results and Contributions

Thomas Morgan's experiments with fruit flies showed for the first time how sex chromosomes can have genes linked to them. He also showed that many genes can be linked together and be inherited together. This helped us to further understand how genes are passed on and inherited, and expanded the earlier ideas of genetics.

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