The Austrian monk Gregor Mendel (1822–1884) laid the foundations for genetics with his pea experiments.
He was an innovator in using mathematics in biology. His contemporary biologists did not recognize the importance of his work because his findings were against popular ideas of inheritance. In 1800 the idea of «the inheritance of mixture» was admitted: a model in which inheritance is in the form of a mixture of the characteristics of parents to their descendants.

This model did not explain what happened when Mendel crossed a low and high pea plant, obtaining only tall plants or because «self-fertilisation» produced the 3:13:13 ratio of tall and low plants in the next generation.
According to the «mixing model», the descendants were to be of medium height and if there was «self-fertilisation» the descendants must also be of medium height.

It was in 1900 that his work was rediscovered and the chromosomal basis of inheritance was seen: Mendel’s «herediatario factors» were carried on chromosomes.

On February 8, Mendel presented the results of his experiments with nearly 30,000 peas at the Society of Natural History in Brünn (Moravia), proposing his «heritage model«:

• one version of a factor (the dominant form) could mask the presence of another version (the recessive form)
• the two mated factors are separated during gamete production, so that each gamete (waitmatocytoid or egg) randomly received only one factor.
• factors that controlled different characteristics were inherited independently of each other.

In 1866 Mendel published his observations and his model of inheritance, with the title «Experiments on plant hybridization«, with his articles: – «Law of Segregation» and «Law of Independent Assortment«.

Mendel, after finishing college, joined st. Thomas Augustinian Abbey in Brno, where he taught courses in physics, botany and natural sciences at high school and university. He began his decade-long research project in 1856 to investigate inheritance patterns.um

He conducted his experiments with garden peas: «Pisum sativum» as a «model system» since peas have a fast life cycle and produce many seeds, can self-fertilisation and plants are easy to cross.

Bibliography:

Mendel Web: «Gregor Mendel»
http://www.mendelweb.org/

Mendel, Gregor; «Experiments in plant hybridization», meetings of the Brünn Natural History Society; Read at the February 8th, and March 8th, 1865,
Mendel, Gregor. 1866. Versuche über Plflanzenhybriden. Verhandlungen des naturforschenden Vereines in Brünn, Bd. IV für das Jahr
1865, Abhandlungen, 3–47
http://www.esp.org/foundations/genetics/classical/gm-65.pdf

R. A. Fisher, M.A.; Sc.D., F.R.S., «Has Mendel´s work been rediscovered?»;
Reproduced from the Annals of Science, v. 1: 115-137 (1936) 144
Galton Professor of Eugenics, University College, London.
https://digital.library.adelaide.edu.au/dspace/bitstream/2440/15123/1/144.pdf