Thomas Hunt Morgan and the Birth of Modern Genetics

The foundation of genetics began with Gregor Mendel, whose work on garden peas introduced the concept of inherited traits. Although Mendel’s discoveries were published in the 1860s, they went largely unnoticed until they were “rediscovered” in 1900, reigniting interest in heredity.

Among the scientists who helped bring genetics to the forefront was Thomas Hunt Morgan, a zoologist at Columbia University. While many biologists of the early 20th century supported Darwin’s theory of evolution, they remained skeptical of both natural selection and Mendel’s ideas. One of Mendel’s rediscoverers, Hugo de Vries, observed mutations in evening primrose plants in 1886, suggesting that sudden genetic changes, not gradual ones, might drive evolution.

Why Morgan Chose the Fruit Fly

In 1907, Morgan began experimenting with Drosophila melanogaster, the common fruit fly, to explore how traits are inherited. He chose this insect for several practical reasons:

• Thousands could be kept in a small container.
• They reproduced quickly, with a new generation every 12 days.
• Males and females were easy to tell apart.
• Genetic mutations were easily observable.

After three years, Morgan discovered a white-eyed male fly, a genetic mutation that changed everything. Breeding experiments revealed a pattern: females always had red eyes, while only some males showed the white-eye trait.

The Chromosomal Theory of Heredity

In 1910, Morgan introduced the chromosomal theory of heredity, proposing that genes are located on chromosomes, much like beads on a string. He demonstrated that some traits, including eye color and wing shape, were linked to the sex chromosomes, establishing the concept of sex-linked inheritance.

This discovery not only validated Mendel’s work but also provided a mechanism for Darwin’s theory of evolution.

Mapping the Genome Begins

Morgan’s student, Alfred H. Sturtevant, expanded on this research. In 1913, he created the first genetic map, assigning specific traits to exact locations on chromosomes. This breakthrough laid the foundation for future efforts in human genome mapping.

A Legacy That Shaped Modern Biology

Morgan’s work bridged the gap between Mendel’s inheritance laws and Darwin’s evolutionary theory, solidifying the gene as the key unit of heredity. By 1916, Morgan had fully embraced natural selection as part of evolutionary theory. His groundbreaking research earned him the Nobel Prize in Physiology or Medicine in 1933 for identifying the role of chromosomes in inheritance.

His influence didn’t stop there. Of the students trained by Morgan—or by his students—five went on to win Nobel Prizes themselves, carrying his scientific legacy far into the future.

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Key Takeaways for Modern Readers

• Gregor Mendel's early work was the seed for modern genetics but went unnoticed until 1900.
• Thomas Hunt Morgan used fruit flies to uncover how genes are linked to chromosomes.
• His experiments revealed how sex-linked traits are passed on through generations.
• Morgan and his team helped build the first genetic maps, paving the way for human genome research.
• His work unified Mendelian genetics and Darwinian evolution, reshaping biological science.
• Morgan’s discoveries earned him the 1933 Nobel Prize and inspired a new generation of geneticists.