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Between 1856 and 1865, Gregor Mendel conducted breeding experiments using the pea plant Pisum sativum and traced the inheritance patterns of certain traits. Through these experiments, Mendel saw that the genotypes and phenotypes of the progeny were predictable and that some traits were dominant over others. These patterns of Mendelian inheritance demonstrated the usefulness of applying statistics to inheritance. They also contradicted 19th-century theories of blending inheritance, showing, rather, that genes remain discrete through multiple generations of hybridization.

From his statistical analysis, Mendel defined a concept that he described as a character (which in his mind holds also for "determinant of that character"). In only one sentence of his historical paper, he used the term "factors" to designate the "material creating" the character: " So far as experience goes, we find it in every case confirmed that constant progeny can only be formed when the egg cells and the fertilizing pollen are off like the character so that both are provided with the material for creating quite similar individuals, as is the case with the normal fertilization of pure species. We must, therefore, regard it as certain that exactly similar factors must be at work also in the production of the constant forms in the hybrid plants."(Mendel, 1866).

Mendelian inheritance states characteristics are discrete and are inherited by the parents. This image depicts a monohybrid cross and shows 3 generations: P1 generation (1), F1 generation (2), and F2 generation (3). Each organism inherits two alleles, one from each parent, that make up the genotype. The observed characteristic, the phenotype, is determined by the dominant allele in the genotype. In this monohybrid cross the dominant allele encodes for the color red and the recessive allele encodes for the color white.

Mendel's work was published in 1866 as "Versuche über Pflanzen-Hybriden" (Experiments on Plant Hybridization) in the Verhandlungen des Naturforschenden Vereins zu Brünn (Proceedings of the Natural History Society of Brünn), following two lectures he gave on the work in early 1865.

In 1952, Rosalind Franklin and Raymond Gosling produced a strikingly clear x-ray diffraction pattern indicating a helical form. Using these x-rays and information already known about the chemistry of DNA, James D. Watson and Francis Crick demonstrated the molecular structure of DNA in 1953. Together, these discoveries established the central dogma of molecular biology, which states that proteins are translated from RNA which is transcribed by DNA. This dogma has since been shown to have exceptions, such as reverse transcription in retroviruses.