1866: Gregor Mendel publishes his book Experiments on Plant Hybridization
In 1866, Austrian monk Gregor Mendel published the results of his experiments with the common pea plant, Versuche über Pflanzenhybriden (Experiments on Plant hybridization). Mendel's observations were virtually ignored by the scientific community when they were first published however when they were "re-discovered" in 1900 they revolutionised the study of Genetics.
Mendel studied the physical attributes of parent plants and their offspring. Although he was not the first researcher to notice similarities between parents and offspring, Mendel was the first to calculate the frequency of specific traits and to conduct a statistical analysis of this data.
He focused on the inheritance of a few key attributes of the pea plants, such as stem length and seed color. Mendel noticed that the parents' physical traits were not blended together. For instance, a plant with green seeds crossed with a plant with yellow seeds produced plants with either yellow seeds or green seeds, and not yellow-green seeds. Based on this observation, Mendel hypothesized that there were some sort of hereditary "particles" that were shuffled into fresh combinations for each new generation. Now we know that these hereditary "particles" are our genes.
Mendel also noticed that certain traits were dominant, that is, they masked the alternative trait. For instance true-breeding plants with smooth seeds invariably gave rise to plants with smooth seeds, no matter which other plant they were crossed with. Mendel characterized each genetic trait as being composed of at least two alleles eg. two copies of the dominant allele (AA) is associated with the dominant trait. Two copies of the recessive trait (aa) is associated with the recessive trait and a heterozygous pair (Aa) is also associated with the dominant trait. Mendel determined that organisms receive one allele for a given trait from each parent.
