What Mendel Knew

Fundamenta Genetica: The Revised Edition of Mendel’s Classic Paper with a Collection of Twenty-seven Original Papers Published During the Rediscovery Era in Brno in 1865. Moravian Museum. Anthropological Publications (Oosterhout, The Netherlands); also Cz

Selection and Commentary by Jaroslav Krizenecky, with an Introduction by Bohumil Nemec
Published for the Celebration of the Centenary of Mendel’s Discoveries, 400 pp.

The old adage that a prophet is not without honor save in his own country has had two innings in the case of Gregor Mendel. It was in 1865 that that remarkable man founded the science of genetics, for nothing less by way of expression is adequate to describe the way in which he enunciated its principles, the basic correctness of which has been confirmed in every branch of experimental science that has been and can be brought to bear on the subject. Like Athena, sprung fullyarmed from the brow of Zeus, genetics came out of the mind of Mendel after eight years of experimental breeding of peas, and as everything is important that relates to mental acts of creation, it is of interest to consider Mendel’s case.

Before him there were horticulturalists who hybridized plants: Koelreuter, Gaertner, Herbert, Lecoq, and Michura, to whom Mendel gave credit in his paper; but there was little to give them credit for. Their results were inconsistent, contradictory, and chaotic, and the reasons for this were that they did not know what to look for when they selected the material on which they worked. Most important of all, they started by asking questions to which their experiments on such material could not provide clear-cut answers. Mendel avoided all this unsatisfactory muddle by taking two steps which, from the point of view of methodology, were models, and of cardinal importance. In the first place he selected his material in such a way as to have parental pairs that differed in one contrasted character at a time. He found this material in peas, and, having crossed them artificially, he allowed their offspring to pollinate themselves for at least three generations. The results that he obtained were not only constant (whichever character was introduced through the seed-parent or the pollen-parent), but also revealed the appearance of the parental types among the offspring in different numbers which he counted and expressed as ratios.

THIS IS WHERE the significance of his other step can be seen: He had thought out the whole scheme of “Mendelian” segregation and recombination of factors in his head, as a theoretical exercise, on the hypothesis that the characters of the organism are controlled by discrete factors (we now call them genes) which exist in pairs; but the members of these pairs separate from one another (segregate) when the organism forms reproductive cells (eggs and pollen-cells), so that no reproductive cell contains more than one member of each pair of genes. At pollination or fertilization, which is random, pairs of genes are recombined. So, if one parent has genes AA and the other parent has genes aa, the reproductive cells formed by the former contain A, those formed by the latter contain a. When they are crossed, the hybrid has the genetic constitution Aa and its reproductive cells contain A or a. Now when two such hybrids are bred (or one is allowed to pollinate itself), the result is the expansion of a simple …

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