StoryImage( ‘/Images/Story//Auto-img-11400383907528.jpg’, ‘Photo by Dr. Robert A. Hedeen’, ‘Gregor Mendel's simple experiments with the garden pea instigated the science of genetics and answered many of Darwin's questions.’);
At about the same time that Charles Darwin was writing The Origin of Species by Means of Natural Selection, in the late 1850s, an Austrian monk named Gregor Mendel was beginning a series of experiments that would lead to the first real understanding of the mechanisms of inheritance.
Mendel was born into a peasant family in 1822 and, as a boy, entered a monastery where he was able to receive a primary and secondary education. He attended the University of Vienna, where he studied mathematics and science. He wanted to be a teacher, but he failed the tests for a teaching certificate, so he returned to the monastery, of which he eventually became abbot. Mendels experiments, carried out in a garden in a quiet corner of the monastery and ignored until after his death, mark the beginning of the modern science of genetics.
His greatest contribution was to demonstrate that inherited characteristics are carried by factors that are discrete units and that are parceled out in different ways, resorted, in each generation. Mendel called these discrete units determiners, and they eventually became known as genes.
For his experiments in heredity, Mendel chose the common garden pea. The plants were commercially available, easy to raise and grew rapidly. He selected several traits of the pea, such as seed form and color, flower position, pod form and color, and several other easily determined characteristics. He raised many generations of peas until he produced plants that always showed the trait in which he was interested, thus establishing pure strains. He then would cross a plant that always produced round peas with one that always produced wrinkled seeds. In the resulting generation, all of the peas were round, and he concluded that the determiner for round dominated the determiner for wrinkled. He thusly illustrated the law of dominance.
He reasoned that the wrinkled determiner was not lost but just masked by the round factor. He then proceeded to cross two of the first generation round plants to produce the second generation. In this generation, both round and wrinkled peas appeared in a ratio of three round to one wrinkled. He declared that winkled was recessive to round. This explains why two parents who are normally pigmented can produce an albino child. Normal pigmentation is dominant; albinism is recessive.
Going further, he established a second basic law of genetics, the law of independent assortment. He used two characteristics in these experiments. He crossed a plant with round (dominant), yellow (dominant) seeds with a plant with wrinkled (recessive) green (recessive) seeds. In this next generation (the F1 or first filial), all the plants produced round, yellow peas.
He then crossed these F1 plants and was amazed at the results obtained in the F2 generation. Four different types were produced: round yellow, round green, wrinkled yellow and wrinkled green in a ratio of 9:3:3:1. Though some of the F2 plants were the same as the original cross, two new varieties appeared. This showed that the determiners for seed texture and color segregated independently from each other.
Darwin could not determine the source of variations within species. He knew variations supplied the raw material of evolution, but he was at a loss to explain how they occurred. Mendels second law of independent assortment, and much later the understanding of mutations, were the answers that eluded Darwin until his death.
Mendel published his findings in an obscure journal, The Proceedings of the Natural History Society of Brunn. This journal was distributed to libraries all over Europe, but, in spite of this, his work was ignored or overlooked for 35 years. Discouraged, he devoted the rest of his life to his duties as abbot of the monastery, and he received no scientific recognition until some years after his death in 1884.
There are some today who seem to spend their time trying to discredit others. (Babe Ruth did not call his home run shot at Wrigley Field in the 1932 World Series with the Cubs; Davy Crockett did not die at the Alamo but surrendered and was later executed; our first landing on the moon was faked, etc). A few Nabobs of Negativity (as a former vice president called them) today claim that Mendel was a fraud. They allege that the numbers he posted for his ratios are statistically impossible. It could be that when dealing with large numbers and determining their progression, Mendel may have rounded some off. But if that occurred, it in no way alters the fundamental principles of genetics that the vast majority of scientists give Mendel credit for discovering. It is too bad there were no Nobel prizes then.
Dr. Robert Hedeen is a former resident of Marylands eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.
From the Feb. 15-21, 2006, issue