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Start Mendel and the Rules of Genetic Lottery
20 July 2015

Mendel and the Rules of Genetic Lottery

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The year was 1900 and the quantum mysteries inside atoms had begun to be unraveled. However, the sharpest minds on the planet could still not explain how it was possible that a person could have flat feet, but not his parents. Suddenly three scientists, a Dutchman, a German and an Austrian, believed that they had discovered, on their own, how children inherit the physical traits of their parents. And before they could even begin fighting to get this recorded in the history books, it was discovered that their supposed scoop had already been recorded 35 years earlier by an Austrian monk whose research with pea plants had almost passed unnoticed.

That monk was Gregor Mendel (20th  July 1822– 6th January 1884), a man passionate about statistics and gardening. But he was not a mere amateur who discovered the foundations of genetics by chance while cultivating vegetables. He knew what he was looking for and he found it in a very well planned experiment. The monks of his monastery in Brno (now in the Czech Republic) were famous for being meticulous researchers. And living up to that reputation, the abbot allowed Mendel to devote himself to science and gave him two full-time assistants to help him to crossbreed 30,000 pea plants again and again for eight years in a long chain of delicate tests.

German stamp to commemorate the first anniversary of the death of Mendel. Credit: Deutsche Bundespost

Over centuries and centuries both animals and plants were crossbred to obtain more useful races. That primitive genetic engineering was part of the folk-wisdom, but no one understood how it worked. Many scientists of the nineteenth century, including Darwin, thought that the physical traits of parents were mingled in their children, as paint colors blend together. However, a person either inherits the ability to roll his tongue into a U-shape or he doesn’t, but he doesn’t inherit the ability to do it halfway. Mendel studied these types of simple traits in peas with two possibilities (green or yellow seed, smooth or wrinkled, etc.) By crossing plants of the pure yellow variety with those of the pure green type, he expected that half of the crop would be of one color and half the other. But all the hybrids were yellow peas plants. It seemed that in all the children the essence of their green parents had disappeared, but the curious thing was that in the following generation some green peas reappeared looking just like their pure green grandparents: exactly one in four.

Each time he repeated the experiment the same ratio emerged, so Mendel decided to attack the biology problem with his math skills. From that fusion was born a new science –genetics– thanks to his statistical calculations of combinations, which botanists of his country did not understand very well when he published his work in 1866. No one, not even he, knew that this was the ideal complement to Darwin’s recent theory of evolution. In the end Mendel gave up, devoting himself to other things. And the twentieth century had to arrive for the merits of his discovery to be recognized, long after his death.

Mendel discovered that in the genetic datasheet of a pea, the color box is not filled in by blending the colors of both parents, nor with the color of just one. In fact, for these simple features there is a double box, which is filled with one marble inherited from the father and with another from the mother. If one marble says “yellow” and the other “green”, the yellow one prevails, being the dominant trait, and the green one stays hidden until, in one of the following generations, two marbles come together that both indicate green. Similarly, in humans, flat feet may appear in a child but may not appear in either the father or the mother, if both parents carry a marble of that recessive trait, like the green pea plants. All living beings with sexual reproduction have in common this inheritance by lottery and the matching of marbles, which today we call genes. They are like the atoms of genetics.

Francisco Doménech, for Window to the Knowledge

>> Find out more about Biotechnology’s history in “The Century of the Gene. Molecular Biology and Genetics”, an essay by Gines Morata for OpenMind.

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