-
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. -
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 -
Thomas Hunt Morgan and his students study fruit fly
chromosomes. They show that chromosomes carry genes, and
also discover genetic linkage. -
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. -
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 ascribed to a genetic cause. -
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. -
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. -
Frederick Miescher isolates DNA from cells for the first time
and calls it “nuclein -
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. -
Charles Darwin wrote “On the Origin of Species by Means of
Natural Selection, or the Preservation of Favored Races in the
Struggle for Life.”
