Not exactly Chuck Norris: on Gregor Mendel and the laws of genetics

In 1901, three scientists, separately from each other, came to revolutionary insights about the mechanism of heredity - insights that changed the world view of biologists. When the scientists reported their findings to them, they discovered that someone had preceded all three of them. Not in a week, not in a month or even in a year, but in fifty whole years. That man was Gregor Mendel.

Gregor Mendel was born in 1822 in Austria. He was intelligent, diligent and serious - but he had one small problem: he didn't know how to handle pressure. Whenever young Gregor was faced with a stressful event, he would break down. And not just a breakdown: a complete breakdown. In high school, the tests caused him such severe weakness and headaches that he had to stop studying for several months and rest in an isolated area. When he got to university and faced the final exams, he collapsed again. Mendel had to repeat a whole year of studies, he came to the final exams again - and once again he collapsed!

Modern biographers speculate that Mendel's breakdowns were actually severe epileptic seizures brought on by the stresses. Whatever the reason, his extreme reaction to stress affected the entire course of his life. Mandel decided, having no choice, to change direction and become a priest. It is likely that he was a religious person to one degree or another, but probably the significant consideration in this choice was the peace and tranquility of the monastery.

But it seems that even the dull life in the monastery was too lively and turbulent for him. A few days after he entered the monastery, he collapsed again, and the abbot wrote about him:

"Mendel is not fit to become a monk. He is unable to see suffering and sickness. In response to what he faced he collapsed dangerously and I had to release him from all his duties at the monastery."

The abbot, realizing that the new monk was not exactly Chuck Norris, decided to send Mendel to teach math and Latin in a small town. For that matter Mendel had to pass a certification exam. He took the test and...surprisingly, he collapsed. Approached the summer time, and collapsed again. After a year he returned to be tested once more... and collapsed. Five years have passed. Gregor took the same test. and collapsed. He returned to the monastery disappointed and broken.

Mendel settled in the monastery and began conducting biological research independently, in a supportive environment and without any external pressure. Mendel planted 22 varieties of peas, a particularly calm plant as we know, interbred them and followed their seven characteristics such as the length of the pod, the degree of its roughness and so on.

The independent experiments he performed revealed intriguing results. When Gregor crossed a rough pea with a smooth pea, for example, all the offspring of the next generation were smooth. He bred the smooth peas with each other, but in the next generation - the third generation of the experiment - not all the peas were smooth. Rough peas appeared here and there. The meticulous Mendel kept a precise record of the features of the peas and discovered that the rough peas do not appear at random, but always in a ratio of three to one. That is, in the third generation there will always be three times more smooth peas than rough.

Mendel may not have known it, but he was not the first to encounter this phenomenon. Thirty years earlier, a researcher named Thomas Andrew Knight had made hybrids between gray and white peas. In the second generation only gray peas were obtained, and in the third generation both gray and white peas in a ratio of three to one. Nate understood that the gray color was dominant over the white color in the peas, but could not find an explanation for this.

Even Charles Darwin was involved in the hybridization of plants. He crossed plants with symmetrical flowering with asymmetrical flowering, and he also got one symmetrical flower for every three asymmetrical flowers in the third generation. but why?

Gregor Mendel had an answer. He assumed that each trait is represented in a plant by two genes. He had no way of knowing what those genes are and what they actually look like in the cell - but it doesn't really matter. This is a solution based on mathematics, or rather on statistics - and not on biology.

Suppose that in the first generation of peas one parent contains two genes and both give the same instruction: be part. The second parent contains two genes and they also give the same instruction: be rough. Each parent contributes only one gene to the offspring. Hence, each pea in the second generation has two different genes: one that determines that it will have a rough texture, and one that determines that it will have a smooth texture.

Now the pea is in trouble. Her parents bequeathed two genes that give her conflicting instructions, but she can't be 'half rough'. She must choose who she loves more, the father or the mother... Mendel stated that one of the genes will always be a dominant gene over the other and will determine how the trait will be expressed in practice. In this case, the gene that states that the texture is smooth is dominant and therefore all offspring will always be smooth.

But the weaker gene, which Mendel called 'recessive', does not disappear. It is still present in the plant even though it is not expressed. In the next generation, Mendel paired two parents from the second generation, each of whom has one smooth gene and one rough gene. Here it is already a matter of luck and statistics. Out of every four offspring on average, three will receive at least one smooth gene - then they will be smooth, because it is dominant. But every fourth offspring, more or less, will get two identical genes, and both will be rough. In the absence of a dominant gene, the recessive genes take command and the pea will be rough. This solution almost perfectly explains the results of the experiment, and now all the scientists have to do is go out and look for a mechanism in the cell that looks like pairs of genes. This was a dramatic breakthrough in the study of heredity. The earth should have trembled. Researchers in white coats were now to storm their microscopes.

But Gregor Mendel was a shy monk from a quiet monastery, and not a distinguished professor from a prestigious university. He published his research in a remote town of a marginal local scientific society, and no one in the world community took notice of them. Mendel sent forty copies of the article to well-known botanists and only one of them, Karl Nagli, replied. Unfortunately, he steered Mandel in the wrong direction. Nagli suggested that he repeat his experiments on the Kita plant, from the sunflower family. Mendel performed the experiment again, but was unable to reproduce it: the results produced by the chickpea plant were completely different from those of the pea! In retrospect, it turned out that the Kita plant reproduces through asexual reproduction, that is to say - the offspring are perfect copies of the mother, and there is no mechanism of genetic mixing as occurs in sexual reproduction.

Mendel tried to apply the theory he devised to animals as well. Here too he was unlucky: he chose to do the experiments on bees, but chose a species that was unusually violent and stung the monks constantly. Mendel had to destroy the bees and stop the experiment. He abandoned science completely and focused on the affairs of the monastery. At the age of 46 he was elected abbot and in 1884 he passed away at the age of 62. His research remained unknown for many years, and even when it was finally rediscovered it still took decades more for scientists to understand what these 'genes' were, in fact, and where they were located within the living cell.

[Ran Levy is a science writer and hosts the podcast 'Making History!', about science, technology and history. www.ranlevi.co.il]