Gregor Mendel and the Reason I Love Science

Today I celebrate the man to whom I owe much of my professional existence. It’s July 20^th, and on this day Gregor Mendel, the Father of Modern Genetics, was born.
 

Like many Ice Dynamo favorites, Mendel’s story has rural beginnings; in 1822, Johann Mendel was born to a family who had been working their farm for 130 years. And like Ice Dynamo favorite Charles Brush, young Mendel was a bit of an iconoclast. Though he gardened and kept bees from an early age, it soon became clear that his agricultural interest was not the result of tradition. He wanted to understand nature, and his family shouldered the financial burden of sending him to secondary school.

His parents hoped he would return and take over the farm, but Mendel was determined to continue his pursuit of knowledge. He studied physics and math Philosophical Institute of the University of Olmütz (studies which ultimately led to his greatest discoveries). Though he tutored privately, he was unable to finance his own education; his sister gave her dowry to cover tuition.

Mendel’s finances continued to strain, so he became a friar, changed his name to Gregor and persisted with his education free of charge. Twice he tried to become a certified teacher, and both times he failed. Nevertheless, when he returned to his monastery, he threw himself into the investigation of the natural world. During that decade (roughly 1854-1864), he researched phenomena that would become the foundation of modern genetics.

From time immemorial, people have performed selective breeding: pairing together two individuals with a desirable characteristic in the hopes of producing offspring with that same characteristic (e. g., breeding grass-like maize over generations to produce modern-day corn). However, it was thought that breeding produced a general blending of physical characteristics. Observationally, that wasn’t a stupid idea: children usually grow to a height that falls somewhere between their parents’ height.

Some of Mendel’s earliest experiments yielded a surprising result: if you bred plants with yellow peas to plants with green peas, the offspring’s peas weren’t greenish-yellow. All of them were yellow. What’s more, this wasn’t just the case for an isolated characteristic like pea color; it was true of flower position, plant height and four other characteristics.

Mendel persisted. He took the yellow pea offspring and bred them together. One might expect that the offspring of yellow pea plants would produce yellow peas – that the green color had been bred or “blended” out of organisms. The “grandchild” generation showed no yellowish-green peas, no greenish-yellow peas, no mix of yellow and green peas on the same organism . . . but some of them had green peas. In fact, for every three yellow-pea “grandchildren,” there was one green-pea “grandchild.”

Here’s where Mendel’s background in statistics enabled modern genetics: he recognized that 3:1 was a very special ratio. The “children” of the original pair had inherited one “character” (one copy of their genes) from each parent. Furthermore, one “version” (allele) of that heritable unit (gene) was dominant in the presence of the other. In the presence of a yellow pea allele, the peas will be yellow rather than a blended color. 

Astonishingly, these “characters” (genes) didn’t blend together into one indivisible unit – they separated when the “children” made gametes (sperm and eggs). Thus, the “children” had one green pea allele and one yellow pea allele, and could give either to the “grandchildren.” Half of the time, the “grandchildren” would receive a green pea allele from one parent and a yellow pea allele from the other parent. Because yellow is dominant, these “grandchildren” had yellow peas. A quarter of the time the “grandchildren” would get the yellow allele from both parents, but another quarter would get two green alleles. In the latter case, no yellow allele was present to overshadow (dominate) the green allele, so the peas would be green. 

The Law of Segregation – the idea that heritable units are indivisible, and behave in statistically predictable ways – was an historic discovery, but Mendel went still further. He followed two traits; he bred tall yellow-pea plants to short green-pea plants. Unsurprisingly, all the offspring were tall with yellow peas. The question was: if he bred these tall yellow-pea hybrids together, would he get three tall yellow peas for every short green pea?

The short answer was no; the results were a whole lot weirder. He got tall plants with yellow peas, tall plants with green peas, short plants with yellow peas and short plants with green peas. At this point, another person might have thrown up their hands and quit science, but once again, statistics saved the day. Mendel realized the ratio of these four different plants was 9:3:3:1. This meant that the alleles for peas color and plant height still segregated and yielded 3:1 ratios, but pea color alleles segregated independently from plant height alleles. He dubbed this phenomenon the “Law of Independent Assortment.”

As is so often the case, these great ideas were relegated to obscurity. After he died, his monastery’s new Abbott burned his research; the only evidence of his work that survived was a little-known paper published in the Natural History Society of Brno. What is even more tragic is the fact that Charles Darwin published his magnum opus, On the Origin of Species, just six years earlier. Darwin’s central thesis was that individuals had natural variation, and that these variations were heritable. Mendel’s research identified that variation, and showed how it was inherited, yet Charles Darwin never heard of Mendel. Indeed, it wasn’t until the next century that Mendel’s work was rediscovered and properly appreciated.

Mendel’s story is one of tenacity. Despite the disapproval of his family, frequent illness, financial hardship, repeated failures and a dearth of recognition, Mendel was as persistent as he was diligent. Gregor Mendel made me realize why I love science so much: it’s the novelty. When I discover some scientific phenomenon, I open a brand new door into human understanding. I get to be the first to walk through – the first to know something – and I get to usher everyone else in. Nothing else – not fortune, not approbation, not notoriety – offers that kind of exhilaration.