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  Section: Genetics » Mendel's Laws of Inheritance
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Pre-Mendelian experiments

Mendel's Laws of Inheritance
Gregor Mendel's life
Pre-Mendelian experiments
Mendel's experiments
Symbols and terminology
Principle of segregation (law of purity of gametes)
Principle of independent assortment
Mendel's results, chromosome theory and linkage
Molecular basis of Mendel's wrinkled seed character
The rules of probability (product rule and sum rule)
Mendelian genetics in humans
Deviations from Mendel's finding

Gregor Mendel was not the first to conduct hybridization experiments, but he was the first to consider one trait at one time and this was perhaps the secret of his success. His experiments were in fact the extension and development of hybridization experiments on pea conducted by earlier workers like Knight (1799) and Goss (1824).

Among the workers who performed hybridization experiments before Mendel conducted his hybridization experiments on pea, the most important name is that of J. Kolreuter (1733-1806), a German botanist. He performed hybridization experiments in tobacco and compared the hybrids with their parents to demonstrate that the hybrids may resemble one or the other parent or may be intermediate between them. He also showed that both the parents make equal contributions to the hybrids. This he demonstrated by making reciprocal crosses (A♀ x B♂; B♀ x A♂). Another significant observation he made was, that although the hybrids themselves may be fairly uniform, their offsprings exhibit considerable diversity.

Kolreuter used tall and dwarf varieties of tobacco for hybridization and found that all first generation hybrids had intermediate size. These hybrids in the next generation gave plants varying in size from tall to the dwarf parent. Kolreuter could not explain these results and a correct explanation was available only in the early part of the present century in the form of multiple factor hypothesis.

Observations similar to those of Kolreuter were made in the last century by a number of workers. These workers included Gartner (1772-1850), Naudin (1815-1899), and Darwin (1809-1882). They also discovered like Kolreuter (1763) that reciprocal crosses give similar results. However, these workers could not give a numerical treatment to their results, as Mendel did in 1866 and therefore could not understand the mechanism of inheritance. In many of these cases actually the object was only to obtain improved varieties of plants for use in agriculture and horticulture, rather than to understand the mechanism of inheritance.


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