-
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.” -
Discovery: 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. -
Discovery: DNA Isolated
Frederick Miescher isolates DNA from cells for the first time
and calls it “nuclein”. -
Discovery: 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. -
Discovery: Chromosome Theory of Inheritance
Walter Sutton observes that the segregation of chromosomes
during meiosis matched the segregation pattern of Mendel’s -
Discovery: The Word Gene is Coined
Wilhelm Johannsen coins the word “gene” to describe the
Mendelian unit of heredity. He also uses the terms genotype
and phenotype to differentiate between the genetic traits of an
individual and its outward appearance. -
Discovery: Chromosomes Carry Genes
Thomas Hunt Morgan and his students study fruit fly
chromosomes. They show that chromosomes carry genes, and
also discover genetic linkage. -
Discovery: One Gene, One Enzyme Hypothesis
George Beadle and Edward Tatum’s experiments on the red
bread mold, Neurospora crassa, show that genes act by
regulating distinct chemical events. They propose that each
gene directs the formation of one enzyme -
Discovery: DNA Has a Regular Periodic Structure
William Astbury, a British scientist, obtains the first X-ray
diffraction pattern of DNA, which reveals that DNA must
have a regular periodic structure. He suggests that nucleotide
bases are stacked on top of each other. -
Discovery: Jumping Genes
Barbara McClintock, using corn as the model organism,
discovers that genes can move around on chromosomes. This
shows that the genome is more dynamic than previously
thought. These mobile gene units are called transposons and
are found in many species.
