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Hybrid

This English word comes almost directly from the corresponding Latin word hybrida, which, to the Romans, meant a mongrel or an offspring that was the result of mixed breeding and was thus somehow "impure".

At the beginning of the eighteenth century (1700 - 1799), most botanists considered that plants (along with all other organisms) had been created in their current form in biblical times. Linnaeus, the famous Swedish botanist and classifier, based his system of classification on the principle that species were fixed and unchanging, and that the number of species he saw around him, were the same as they had been at the time of Creation.

Unfortunately for Linnaeus, experiments going on all around him, especially those of J.G. Gmelin (a professor of chemistry at the University of Tubingen), were starting to cast doubt on the fixity of plant species.

In 1749, Gmelin gave his friend, J.G. Kolreuter the idea of artificially fertilizing plants and producing "mongrels" or "hybridas", that, at first glance seems to have the properties of new species. Kolreuter believed that two fluids, one from each parent, at first blended into and intermediate condition in their offspring. Later, however, when the juvenile grew up into the adult form, the two fluids somehow separated again.

After Kolreuter's death, an apothecary from Brunswick, A.F. Wiegmann won a prize for his investigations into plant sex and work on constructing pea hybrids. Wiegmann showed that hybrid pea plants were not a "mixture" but somehow looked either like the paternal parent or the maternal parent, but not both. Unfortunately, this observation was clouded by the appearance of traits seen in neither parent, and he never satisfactorily made the connection between the results he was getting and what might be causing them.

Certainly Mendel's experiments and work was the direct successor to these ideas and those of the German botanist F.C. Gartner who published, in 1849, a large monograph on plant hybridizations, in which he not only repeated Kolreuter's work, but extended it through 10,000 artificial fertilizations in over 700 plant species.

Despite all this preceding work, when our Brother Gregory picked "plant hybridization" as his research topic, three nagging questions still remained; why were plant hybrids often infertile can could not be bred again, what form (phenotype) did the hybrid take (one parent, both parents or something new?), and what, if anything, was controlling the appearance of the hybrid?

These were not easy questions, and their answers had eluded many great minds before Mendel's.

Part of his genius can be seen in the way he set about answering these questions, and in the way in which he planned his experiments. The infertility question led him to the Leguminosae and Pisum sativum - the common, garden pea plant - which showed none of these problems. Pisum, he states, yields fertile hybrids and that the pollinated flower can be easily protected from cross pollination. Almost as an afterthought, he adds that the plants are easy to cultivate and can be grown in gardens and greenhouses.

He answered the "phenotype" question by also picking for study characteristics in the seeds and plants that are "easily and reliably distinguishable". Such characteristics had to be uniform, unambiguous, easily seen and not subject to variation. Flower color was a good example. Pea flowers were either purple (a reddish color) or white. These two "characteristics" could be easily seen and positively distinguished from each other. There was no question that a particular plant had either purple or white flowers.

The final question of the "mechanism" controlling appearance or form, had to wait another hundred years, but Mendel's research ruled out one possible mechanism and clearly laid the groundwork for the branch of natural science named after him; Mendelian Genetics.


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© 1999 Professor John Blamire