Drosophila: Thomas Hunt Morgan
Around 1908, Thomas Hunt Morgan began to explore the genetics of what was to become a model organism, Drosophila melanogaster (Fruit fly). This small organism had a relatively short life cycle, great fecundity and was easily managed. From these flies that normally have red eye coloring, he and his students found white-eyed mutants. The lab noted that white-eyed flies were almost exclusively male. This gender imbalance lead Morgan to believe that the trait was sex-linked. In 1911, Morgan published a paper that described the inheritance patterns of 5 eye-colors in Drosophila (Morgan, 1911).
While DNA was not yet known as the source of genetic information, Morgan’s studies revealed that the location of genes most likely resided on the chromosomes. By cataloging many mutations in the lab, he was able to construct a map of gene locations. His 1922 paper specifically stated that some traits were sex-linked and therefore residing on the sex chromosome. When performing crosses of white-eyed males to wild-type females, he continued to find white-eyed trait only in males. However, in the subsequent cross of females from that generation with white-eyed males, the presence of white-eyed males and females were revealed. This indicated that the white-eyed trait was recessive and resided on the X chromosome.
Morgan received the Nobel Prize in Physiology or Medicine in 1933 for his inference of chromosomes being a physical mechanism for packaging genetic information in the cells.
- Morgan TH. THE ORIGIN OF FIVE MUTATIONS IN EYE COLOR IN DROSOPHILA AND THEIR MODES OF INHERITANCE. Science. 1911 Apr 7;33(849):534-7
Secrets of the X-Chromosome
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