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Natural Selection
Charles Darwin wrote “On the Origin of Species by Means of
Natural Selection, or the Preservation of Favored Races in the
Struggle for Life.” -
Heredity Transmitted in Units
Gregor Mendel’s experiments on peas demonstrate that
heredity is transmitted in discrete units. The understanding
that genes remain distinct entities even if the characteristics
of parents appear to blend in their children explains how
natural selection could work and provides support for
Darwin’s proposal -
DNA Isolated
Frederick Miescher isolates DNA from cells for the first time
and calls it “nuclein”. -
Mitosis Described
Walter Flemming describes chromosome behavior during
animal cell division. He stains chromosomes to observe them
clearly and describes the whole process of mitosis in 1882. -
Rediscovery of Mendel’s work
Botanists DeVries, Correns, and von Tschermak independently
rediscover Mendel’s work while doing their own work on the
laws of inheritance. The increased understanding of cells and
chromosomes at this time allowed the placement of Mendel’s
abstract ideas into a physical context. -
Chromosome Theory of Inheritance
Walter Sutton observes that the segregation of chromosomes
during meiosis matched the segregation pattern of Mendel’s -
Orderly Inheritance of Disease
A British physician, Archibald Garrod, observes that the
disease alkaptonuria is inherited according to Mendelian rules.
This disease involves a recessive mutation, and was among the
first conditions givin to a genetic cause. -
Chromosomes Carry Genes
Thomas Hunt Morgan and his students study fruit fly
chromosomes. They show that chromosomes carry genes, and
also discover genetic linkage. -
DNA Transforms Cells
Oswald Avery, Colin MacLeod, and Maclyn McCarty show
that DNA (not proteins) can transform the properties of cells -- clarifying the chemical nature of genes. -
Genes Are Made of DNA
Alfred Hershey & Martha Chase show that only the DNA of a
virus needs to enter a bacterium to infect it, providing strong
support for the idea that genes are made of DNA