Thomas Morgan and his contributions to genetics

Thomas Hunt Morgan was an American pioneer in the fields of genetics and embryology. He is best known for his studies of mutation in Drosophila melanogaster, more commonly known as the fruit fly. Morgan's studies on mutations among the fruit flies showed that genes were carried in chromosomes, and therefore, genes were the basis of heredity. Morgan's work formed the basis for the modern study of genetics. In recognition of his achievements, Morgan was awarded the Nobel Prize in Physiology or Medicine in 1933.

Early influences

Morgan was born on September 25, 1866, to a family that was considered southern royalty. He was descended from illustrious families, with ancestors including Confederate General John Hunt Morgan, millionaire John Wesley Hunt and great-grandfather Francis Scott Key. However, the family's fortune turned after the Civil War, and lost much of their property (Allen 2000).

This experience partially pushed Morgan into the sciences, rather than the political and business pursuits of his family. Morgan entered the State College of Kentucky at the age of 16, where he studied natural history. During the summer, Morgan also worked with the federal geological survey. He earned his Bachelor of Science in 1886, graduating as class valedictorian (Allen 2000).

Morgan decided to pursue graduate studies in Biology, and entered Johns Hopkins University, one of the few universities at the time that had an extensive biology program. It was here that Morgan met and studied under famed embryologist and morphologist William Keith Brooks. Under Brooks' tutelege, Morgan was able to undertake experimental work and was able to co-author several important publications. Despite tight finances, Morgan was able to secure a fellowship large enough to help him finance his studies. He eventually earned his Doctorate in Philosophy in 1890 (Allen 2000).

Work in embryology year after earning his PhD, Morgan accepted a teaching position at Bryn Mawr College. It was here where he began to analyze the development of embryos from separated blastomeres. His work also included the study of fertilization in nucleated and non-nucleated egg fragments (Shine and Wrobel 1976). In addition to fueling his professional work, Bryn Mawr was also where Morgan met graduate student Lillian V. Sampson, a cytologist and embryologist who eventually became his wife.

The early 20th century ushered in considerable interest in Charles Darwin's theory of evolution, and Morgan was no exception. While Morgan agreed with evolution as a given, he wanted to know more about how natural selection occurs. The future Nobel Prize winner was interested in further explanations on the role of heredity in the transmission of variations among the species.

Morgan was also interested in the work of geneticist Georg Mendel, who studied chromosomes. In 1910, Morgan publicly disagreed with the prevailing notion in embryology, that a fully-formed adult was already locked inside the ova or sperm cell. Rather, Morgan argued that there was no single chromosome that guaranteed the heredity of specific traits (Shine and Wrobel 1976).

Drosophila

In 1903, Morgan accepted the first professorship in experimental zoology at Columbia University. He moved his family to New York and began to work in genetics, fueled by his interest in the gaps in the work of Darwin and Mendel. During this time, scientist Hugo De Vries, a geneticist, revisited the work of Mendel and again proposed that new species were created as a result of mutations. Morgan then set out to prove De Vries' theory, using his now-famous Drosophila experiment.

Morgan used X-rays to mutate samples of Drosophila and cross-bred the mutants to regular samples. In 1910, Morgan found a male fly with white eyes, a mutation from the typical red eyes. However, after breeding the white-eyed fly with a red-eyed female, Morgan discovered that the resulting spawn all had red eyes. To Morgan, this suggested that the white-eye trait was a recessive trait. Later, Morgan found and tracked the results of other mutations, such as pink eyes and mutant wings (Shine and Wrobel 1976).

These findings eventually formed the basis for Morgan's theories on genetic linkage. He believed that the mutant traits were carried in specific chromosomes and most likely, sex-linked. He later demonstrated that the genes identified by Mendel can be located in a chromosome map (Morgan 2002).