In 1865, the Austrian monk Gregor Mendel published Experiments in Plant Hybridization, the first paper to provide mathematical analyses for patterns of inheritance.  Mendel's studies with pea plants were the first to relate the outward appearance of an organism (phenotype) to its genetic composition (genotype).  His work established a set of
                      laws governing the inheritance of traits from
                      one generation of organisms to the next:
 

1.  Each characteristic is governed by a pair of "factors"
     (genes).  If one of this pair always expresses it self, it is
     said to be a "dominant" trait.  A trait which does not
     express itself when paired with a dominant is said to be a
     "recessive" trait.

2.  Parental genes for each trait are separated one from
     another during the formation of gametes (sex cells) and
     are "segregated" one from another, such that each gamete
     contains only one of the pair, and each is equally likely
     to occur in gametes.

3.  Genes for each trait "assort independently" of one another
     during gamete formation, such that any combination of
     gene combinations is equally likely to occur.

Mendel's work was lost and unrecognized until 1900, when the Dutch and German scientists Hugo de Vries and Carl Correns rediscovered and confirmed it through experimentation.