This year marks the 175th anniversary of the birth of the great Austrian scientistmonk Gregor Mendel, who is venerated as the father of modern genetics.
Mendel was born in 1822 of peasant parents in Moravia (now part of Czechoslovakia). He studied for a short period at the Institute of Olmutz, but had to leave for financial reasons, and became an Augustinian monk at the monastery at Brno.
He studied mathematics and natural history in Vienna to become a high school science teacher in Brno. In his spare time he studied the results of making crosses between different varieties of garden peas.
Mendel's interest had been sparked by observations of the results of the hybridisation of ornamental plants to produce new varieties. He noted the regularity of the results and he wondered what would happen if the hybrids were crossed.
Garden peas were available in pure-breeding varieties. They reproduce sexually and the reproductive organs are enclosed within the petals so that self-pollination (fertilisation) normally takes place. However, the plants can easily be cross-pollinated artificially.
Mendel studied 22 varieties in experiments extending over eight years. To illustrate some of the results he achieved let us consider his studies concerning the position of the pea-flowers on the stem.
Mendel used two varieties of pure-breeding plants. In one variety the flowers always had an axial distribution, i.e., along the main stem. In the other variety the flowers always had a terminal distribution, i.e., bunched at the top of the stem.
Mendel cross-pollinated the two varieties and examined the progeny - called the F1 generation. The parent plants are called the P1 generation.
The cross-pollination was carried out as follows. The male and female sex organs of the plant are enclosed within the flower. The tip of the male organ is called the anther, which produces the male sex cell - the pollen. The pistil produces the egg cell.
Mendel removed the anthers of an immature flower of one variety and covered the flower with a small bag to prevent stray pollen from landing. When the female portion was mature, Mendel transferred pollen from the alternative variety and again covered it.
He found that all the plants in the F1 generation were of the axial flower variety.
To find what had happened to the hereditary factor for terminal flowers, Mendel allowed self-pollination of the F1 plants to produce second-generation (F2) plants. In this generation he found that some of the plants were of the terminal flower variety. The ratio of plants with axial flowers to plants with terminal flowers was 3 to 1 (actually 3.14 to 1).
Mendel reasoned that there are two factors in each plant for flower position, but only one of the two factors is carried by a pollen grain or an egg. When pollination occurs, the number of factors is restored to two.
The pure-breeding P1 plants with axial flowers contained two factors for the axial position. The pure-breeding P1 plants with terminal flowers contained two factors for the terminal position.
The plants in the F1 generation contained both factors, but all of these plants had axial flowers. Therefore, the factor for axial position must be dominant over the factor for terminal position, which Mendel termed a recessive factor. When F1 generation pollen grains and eggs are formed, some carry the factor for axial flower position and some the factor for terminal position. If these plants are allowed to self-fertilise, it will produce a random mixture of the two factors.
Some seeds get two factors for axial position, some get a factor of each kind, and some get two factors for terminal flowers. Mendel calculated by mathematical probability that one quarter of F2 plants would be of the first kind, one half of the second kind, and one quarter of the third kind.
The factor for axial flowers is dominant. Therefore the first two groups have axial flowers and only the third group has terminal flowers, i.e., three fourths of the plants should have axial flowers and one fourth should have terminal flowers. Mendel got an experimental ratio of 3.14 to 1, very close to the mathematical expectations.
Apart from flower position, Mendel used six other pairs of alternative traits in his experiments (e.g., round and wrinkled seeds, long and short stems etc), and found that all behaved in the same manner, i.e., gave a three to one ratio of dominant to recessive traits in the F2 generation. Each of the ratios differed slightly from three to one, but not enough to raise any serious doubts.
Mendel used large numbers of F2 plants, which was very important. Had he used smaller numbers the results might have deviated more from the mathematical expectation. Such results would be difficult to analyse.
In his experiments, across all seven pairs of traits, Mendel made 14,889 observations of dominant traits and 5,010 observations of recessive traits in the F2 generation - a ratio of 2.98 to 1, which is as close to a three to one ratio as you could hope to achieve under experimental conditions where chance assortment is involved.
The modern word for Mendel's factors is genes. Mendel's interpretation for what happens in such a cross is today accepted as the correct analysis not only for plants but also for animals.
Mendel's system was to represent dominant genetic factors using a capital letter for the dominant gene and the same letter in the lower case for the recessive alternative. The letter is the first letter in the trait which is less common.
For flower position, T means axial and t means terminal. That nomenclature is still in use today, e.g., h for the haemophilia gene (bleeder's disease) and H for the alternative dominant gene that is associated with normal blood-clotting.
Of course, it has been known from time immemorial that characteristics are inherited from generation to generation, but until Mendel's brilliant work nobody understood the mechanism of inheritance. Mendel's identification of the fundamental factors that determine an organism's characteristics and how these factors (genes) can independently sort and segregate from generation to generation was a revolutionary breakthrough.
Mendel reported his results at a meeting of the Association for Natural Research in Brno in 1865 and published the work that same year in a book under the title Treatises on Plant Hybrids. The work was ahead of its time and was not appreciated by the wider scientific community (nor indeed was it widely read).
In 1900 there was a famous rediscovery and appreciation of Mendel's work by Carl Correns in Germany, Hugo de Vries in Holland and Erich von Tschermak-Seysenegg in Aus tria.
Mendel's work laid the firm foundation for the modern science of genetics. The rise of molecular biology in this century identified the chemical nature of the gene as DNA and demonstrated how the gene determines characteristics - by controlling and specifying what proteins are synthesised. We are now in the middle of a spectacular explosion of genetic-based developments.
Mendel's experiments stand up. He achieved almost perfect results because he was simply that good. Pure genius.
Mendel was disheartened by the lack of response to his published work. He was elected as abbot of the monastery in 1868. The heavy workload of running the monastery took him away from his beloved experiments.
Shortly before his death in 1883 he said: "My scientific studies have afforded me great gratification, and I am convinced it will not be long before the whole world acknowledges the results of my work." Seventeen years later his prediction came true.
William Reville is a senior lecturer in biochemistry at UCC