A Historical Timeline: Cracking the Code of Life

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1910
Thomas Hunt Morgan and his team at Columbia University, and later CalTech, begin studying hereditary traits in Drosophila fruit flies. Their research reveals how genes are arranged in a row on chromosomes, as well as a variety of other genetic phenomena including sex-linked traits (traits that are passed only to one sex and not the other), the effect of a gene's location on its functioning, the existence of multiple alleles (gene forms), and chromosomal inversion (the reversal of a sequence of genes along part of a chromosome). Morgan's experiments also lead to Drosophila's unusual position as one of the best-studied organisms and most useful tools in genetic research to this day.

1926
Hermann Müller, a former member of Morgan's team, shows that exposure to X-rays can cause genetic mutations in Drosophila.

1941
While experimenting on bread mold, George Beadle and Edward Tatum show that genes regulate specific chemical events. They suggest that each gene directs the formation of one particular enzyme.

1944
Barbara McClintock, while studying the inheritance of color and pigment distribution in corn kernels at the Carnegie Institution Department of Genetics in Cold Spring Harbor, New York, discovers that genes can move from place to place on a chromosome and even jump from one chromosome to another. McClintock's discovery of transposable, or movable, genetic elements was greeted with initial skepticism but later recognized when, at age 81, she was awarded a 1983 Nobel Prize. Scientists now believe transposons may be linked to some genetic disorders such as hemophilia, leukemia, and breast cancer. They also believe that transposons may have played critical roles in human evolution.

Oswald Avery, Colin MacLeod, and Maclyn McCarty of the Rockefeller Institute show that a molecule in the cell nucleus called deoxyribonucleic acid, or DNA--and not proteins, as previously believed--contains the factors that determine heredity in most organisms.

1952
Rosalind Franklin, a British chemist, uses a technique called X-ray diffraction to capture the first high-quality images of the DNA molecule.

1953
Franklin's colleague Maurice Wilkins shows the pictures to James Watson, an American zoologist, who has been working with Francis Crick, a British biophysicist, on the structure of the DNA molecule. After several false starts, Watson and Crick conclude that DNA is a double helix--two spiral strands that wind around each other like a twisted rope ladder.

1958
François Jacob and Jacques Monod predict the existence of messenger RNA, the molecule that carries information from the DNA in the cell's nucleus to the protein factories (the ribosomes) in the cytoplasm.

1962
Crick, Watson, and Wilkins share the Nobel Prize in medicine and physiology for the discovery that the DNA molecule has a double-helical structure. Rosalind Franklin, whose images of DNA helped lead to the discovery, died of cancer in 1958 and, under Nobel rules, was not eligible for the prize.

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