Next year (2000) scientific genetics will celebrate hundred years anniversary of its birthday. It was born in the year 1900 by the discovery of the work by Gregor Mendel the monk in the Brno monastery.

Johann Mendel was born in the village Hyncice on July 22, 1822 in the family of Moravian peasant. His education was taken care of by local priest Father J. Schreiber. Young Johann was very successful in schools, but the family cannot support him in further study. Therefore his teacher Schreiber persuaded Abbot Napp to admit young student to the Brno monastery. Aged twenty-one Mendel became cleric and assumed the name Gregor.

Mendel was liked as a teacher, however, ironically, he failed his teacher’s examination due to his weakness in biology. This was why Abbot Napp sent him to Vienna to study physics, chemistry and mathematics. His teacher in physics was Professor Christian Doppler (known by his explanation of an effect that has been called by his name). This study was critical experience that leads later to the correct interpretation of the laws of heredity.

After coming back to Brno Mendel started the study of heredity as it was the request of Abbot Napp. He wanted to help breeders in the Moravia region who were puzzled by the lack of recognisable patterns of inheritance. Particularly they were confused by the fact that certain trait disappeared during breeding in order to reappear later again.

Mendel selected garden pea as an experimental object. Thanks to the training in chemistry he considered it necessary to select simple traits of clear binary nature: flowers white or red, seeds round or wrinkled, seeds green or yellow. Knowing that chemicals used in an experiment must be pure, he crossed the selected plants as long as the trait was stable in repeated crosses. Thus he started with pure lines.

Then Mendel crossed his pure lines, e.g. plants with round seeds and wrinkled seeds. The offspring had all round seeds. The trait wrinkled had disappeared. The offspring of first cross is called first generation, F1. When let the F1 generation plants self fertilize Mendel obtained the second generation F2. Surprisingly wrinkled seeds were again present. Here his training in physics came again forward: he started to count the round and wrinkled seeds and found that about three round seed were per one wrinkled one. He observed similar results when peas with red flowers were crossed with white flowering plants. White colour was absent in F1 but occurred again in F2 in the ratio 1 to 3 red flowering plants.

Looking for the hypothesis how to explain such results Mendel used the thinking of a chemist: the properties of substances are given by the ratio of simple elements. The offspring of a cross must have two different elements – one from the mother and one from the father. He found, that these elements preserve their individuality, they do not mix since the cross between white an red colour has never be a pink colour. Consequently one of the two elements is "stronger”, dominant and the other "weaker", recessive. Now these two alternatives are called alleles. The recessive allele is hidden, but still exists and by crossing F1 individuals it is transferred to the F2 where free mixing of alleles takes place and at random segregate in pairs as can be presented like this (white and red)

(wr) X (wr) (ww) + (wr) + (rw) + (rr)

As the red allele is dominant all combinations containing it have red flowers. It can be seen why the white colour – a recessive trait - appeared again: one out of four combinations is formed by a pair of recessive alleles. Mendel verified this scheme by self-pollination of white plants and self-pollination of red plants obtained in F2. Only white plants occurred in the former experiment whereas both red and white resulted in the latter. He explained the result by considering the white plants as homozygous what means that they have two identical alleles. The red were both homozygous (one third of red) and heterozygous (two thirds) carrying two different alleles and gave, as shown above, homozygous recessive white flowers when self-pollinated.

This was clear explanation of the unexplained disappearance and reappearance of certain traits. In the next issue we shall describe other experiments that Mendel executed in the garden of the monastery in Brno. He published his results in a very obscure journal Verhandlungen in the year 1865. Scientists were not aware of his discoveries for 35 years. In 1900 three researchers Hugo de Vries, Karl Correns and Erich von Tschermak performed similar experiments and before publishing their results they made deep search in the literature. They were shocked finding the Mendels’ results and presented them for the scientific community. This is why the year 1900 is considered to be the birth of scientific genetics.

This time we learned following terms: