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Mendel, Gregor (Johann)

characters law alleles mendel’s

(1822–84) Austrian botanist: discovered basic statistical laws of heredity.

In the long term Mendel was certainly successful; he laid a foundation for the science of genetics. In another sense he was a failure; he did not succeed in examinations and his research was largely ignored until 16 years after his death.

A peasant farmer’s son, he entered the Augustinian monastery in Brno (then in Moravia, now the Czech Republic) when he was 21 and was ordained 4 years later. He became a junior teacher and during the 1850s twice tried to pass the teachers’ qualifying examination. From 1851 he was sent by his order to study science for 2 years in Vienna, and afterwards he began his plant-breeding experiments in the monastery garden. He was elected abbot in 1868, which left him little time to continue this work; in any event his personality and reputation were unsuited to publicize his scientific ideas and most biological interest was directed elsewhere. Mendel’s work had to await rediscovery by and others to become appreciated, in 1900. Even then it needed the vigorous advocacy of , and many plant and animal breeders, to be accepted.

Mendel’s famous work on the inheritance of characters was done on the edible pea ( Pisum spp.), in which he studied seven characters, such as stem height, seed shape and flower colour. The plants were self-pollinated, individually wrapped (to prevent pollination by insects) and the seeds collected and their offspring studied. The characters were shown not to blend on crossing, but to retain their identity. Mendel had a gardener’s skill and his experiments were excellently organized. He found that the characters were inherited in a ratio always close to 3:1; he theorized that hereditary elements or factors (now called genes) exist that determine the characters, and that these segregate from each other in the formation of the germ cells (gametes).

His results of 1856 are summarized in two laws, expressed in modern terms as follows. The characters of a diploid organism are controlled by alleles occurring in pairs. Of a pair of such alleles, only one can be carried in a single gamete. This is Mendel’s First Law, or the law of segregation. We now know, although Mendel did not, that this law follows from the process of meiosis and the physical existence of alleles as genes. He also found that each of the two alleles (ie the two forms) of one gene can combine randomly with either of the alleles of another gene (Mendel’s Second Law, or the law of independent assortment). Genetics has both confirmed and refined Mendel’s laws; work showed how linkage and crossing-over modify the second law.

Mendel was disappointed that his work aroused little interest and he sent his paper to , the leading German botanist, who advised him to experiment with more plants; Mendel had already studied 21 000. Curiously, when in 1936 studied his results, he found they are statistically too ideal; possibly because a few intermediate plants occur, which Mendel classified to accord with his expectations. Or, perhaps, an assistant tried too hard to be helpful.

Mendelayev, Dmitri Ivanovich [next]

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