Mendel, Gregor Johann (1822–1884)

Mendel's laws explain the proportion of offspring having various characteristics. When pea plants having smooth yellow peas are crossed with plants with wrinkled green peas, the first-generation offspring all have smooth yellow peas. The second-generation offspring, however, contain smooth yellow, wrinkled green, smooth green, and wrinkled yellow peas. This can be understood by tracing the passage of alleles Y, S, s, y throughout the generations. S and Y are dominant genes.

Austrian biologist who founded genetics. His experiments with successive generations of peas gave the basis for his theory of particulate inheritance rather than blending, involving dominant and recessive characters; see Mendelism. His results, published 1865–69, remained unrecognized until the early 20th century.

Mendel formulated two laws now recognized as fundamental laws of heredity: the law of segregation and the law of independent assortment of characters. Mendel concluded that each parent plant contributes a ‘factor’ to its offspring for determining a particular trait. These are what we now recognize as genes or alleles. He showed that the pairs of factors in the offspring do not give rise to a blend of traits.

Much of his work was performed on the edible pea Pisum, which he grew in the monastery garden. He carefully self-pollinated and wrapped (to prevent accidental pollination by insects) each individual plant, collected the seeds produced by the plants, and studied the offspring of these seeds. Seeing that some plants bred true and others not, he worked out the pattern of inheritance of various traits.

He reported his findings in ‘Experiments with Plant Hybrids’ (1866), but the importance of his work was not recognized at the time, even by the eminent botanist Karl Wilhelm von Naegeli, to whom Mendel sent a copy of his paper. It was not until 1900, when his work was rediscovered by Hugo De Vries, Carl Erich Correns, and Erich Tschermak von Seysenegg, that Mendel achieved fame – 16 years after his death.

Biography Mendel was born in Heinzendorf (now Hyncice in the Czech Republic), and entered the Augustinian monastery in Brünn, Moravia (now Brno, Czech Republic) in 1843. Later he studied at Vienna. In 1868 he became abbot of the monastery. His experiments breeding peas gave the basis for his theory of particulate inheritance rather than blending inheritance.

Mendel's experiments Seeing that some plants bred true (always produced identical offspring, identical to the parent plant) Mendel decided to investigate the results of crossing two varieties with different characteristics, for example tall and dwarf pea varieties. Having carefully self-pollinated and wrapped each individual plant, collected the seeds produced by the plants, and studied the plants that grew from these seeds, he found that dwarf plants produced only dwarf offspring and that the seeds produced by this second generation also produced only dwarf offspring. With tall plants, however, he found that both tall and dwarf offspring were produced and concluded that there were two types of tall plants, those that bred true and those that did not.

Next he cross-bred dwarf plants with true-breeding tall plants and found that all the offspring in the first generation were tall but that the offspring from subsequent generations were a mixture: one-quarter true-breeding dwarf plants, one-quarter true-breeding tall plants, and one-half non-true-breeding tall plants.

Mendel also studied other characteristics in pea plants, such as flower colour, seed shape and flower position, finding that, as with height, simple laws governed the inheritance of these traits.