How Gregor Mendel set the stage for our greatest scientific discovery
The monastery as a center of science
In the mid-1850s in a small town called Brno, then part of the Austrian Empire, an Augustinian monk named Gregor Mendel was quietly tending peas in the garden of the St. Thomas Monastery.
A few years earlier Mendel had completed his studies at the University of Vienna in mathematics and physics under Christian Doppler (who discovered the Doppler effect which we use today to measure the speed of cars and galaxies), and botany under Franz Unger (who hypothesized that some unknown components within plant cells determined their heredity, and proposed a theory of evolution prior to Darwin’s publication of On the Origin of Species).
Mendel’s gardening in Brno wasn’t your typical puttering in the dirt. This was actually a large experiment covering almost 5 acres of the monastery’s gardens, approved by the Abbot, Cyril Napp, in 1854. Mendel’s goal was to understand how hereditary characteristics were passed along in successive generations of hybrid progeny. At the time, the differing traits of the parents were believed to be blended in the offspring, but that eventually after many generations the hybrid would revert to the original parental form. But no rigorous tests were done to challenge or confirm that hypothesis, and Mendel meant to rectify that experimental deficiency.
Today we associate Mendel with homework exercises using Punnett squares to determine probabilities of trait dominance. But perhaps Mendel’s most important contribution aside from establishing the field of genetics, is the use of quantitative statistical methods and large sample sizes to probe biological questions. Biology at the time was typified by Darwin’s bushwhacking field work around the world aboard the HMS Beagle from 1831-36, or Thomas Henry Huxley’s more sedate Victorian benchwork of comparative anatomy. Mendel was the first to apply the tools of math and physics that he learned from Doppler and others at Vienna to the fundamental questions of biology.
Mendel’s beginnings
Mendel’s opportunity to study with such eminent scientists and academics was not a given. He was born Johann Mendel on July 22, 1822, the only son of Anton and Rosine Mendel. He had an older sister Veronika, and a younger sister Theresia. They were a poor farming family in the village of Heinzendorf in what was then called Silesia of the Austrian Empire (now the Czech Republic). He was lucky that a local teacher and priest recognized Mendel’s talents and recommended that his parents send the 11-year-old Johann to grammar school (Gymnasium), first in a neighboring town and then in the big city of Troppau.
The new school was a financial burden for the family, and hard on Johann who had to take four months off due to illness, perhaps from stress and loneliness. Nonetheless Mendel graduated with honors in 1840 and went on to enroll in a two-year program at the University of Olmutz where he excelled in math and physics. Again, problems with finances and depression burdened Mendel (Theresia gave him her dowry to pay for expenses, but he had to take a year off to regain his health), yet despite these challenges he graduated from the Philosophical Institute in 1843. Mendel’s father wanted him to take over the farm upon graduating, but instead he joined the Augustinian order of monks where he was given the name of Gregor. Since the friars paid for his education and his living expenses, this spared him from tremendous financial anxiety, and also paved his path towards further education.
How Mendel’s family shaped his life
While Anton unknowingly instilled in young Johann the skills and work ethic needed to thrive in his future scientific endeavors, the women in Johann’s life were even more important in many ways. Anton’s wish was for Johann to return to the family farm after his education and to eventually take over from him. But Johann’s mother Rosine is believed to be the driving force behind his going forth and out of Heinzendorf to be educated to his full potential, for a chance to improve his life beyond the farmers his family had always been.
Rosine’s father, Martin Schwirtlich, was one of a long line of professional gardeners who tended the estates of nobles. But one of Rosine’s uncles, Anton, established and ran an elementary school in Heinzendorf from 1780 to 1788. There were some problems with the school after Anton Schwirtlich’s death and the school was not re-established again until 1796. Thomas Makitta was its first teacher in this new incarnation, and it was Makitta who first recognized Johann’s potential. The village priest, Father Schreiber, played a role in the children’s education, and it was Makitta along with Schreiber who convinced Anton and Rosine to send Johann off for further education, first to the neighboring town of Lipnik which possessed a higher elementary school, and eventually to the city of Troppau. Since Johann’s father Anton was feudally obligated to spend three days a week working on the estate of the Countess Truchsess-Ziel, Anton made very little income from his farm that he could spare for Johann’s education. At one point, Mendel’s younger sister Theresia, donated her dowry for his educational expenses. Mendel felt this generosity so deeply that he later helped to support Theresia’s two sons who eventually became doctors.
Mendel’s plans for his peas
Mendel did not jump immediately into his experiments once Abbot Napp gave his approval in 1854. He spent the next couple years selecting and understanding his experimental model, the pea (Pisum savitum), which was an excellent choice since it matures and reproduces rapidly, has obvious traits, and is easy to artificially fertilize as well as to protect from accidental fertilization. Mendel then further selected peas with lineages that displayed a single clear and defining characteristic and chose seven contrasting traits:
· seed shape (smooth versus wrinkled)
· seed color (green versus yellow)
· seed coat color (gray versus white)
· pod shape (full versus constricted)
· pod color (green versus yellow)
· flower distribution (along stem versus end of stem)
· plant height (tall versus short)
He then spent the next two years confirming that these traits did not vary, that they were stable and controllable from generation to generation.
Mendel’s peas bear fruit
Finally, in 1856, Mendel began his experimental crosses, using a very fine paint brush to carefully transfer pollen from one lineage to artificially fertilize another, then characterizing and counting the resulting hybrids. Over about eight years, he characterized tens of thousands of pea plants in his garden.
After Mendel carefully made his crosses, he waited for the peas to bear fruit, planted the next generation of peas, and then the magic of science itself finally began to bear fruit. He characterized the progeny according to their traits; if one parent had smooth seeds and the other had rough seeds, what did each offspring have? And then he counted them. He did this over and over. For each set of traits, crossed one to the other, and then the other way around. Painting the pollen from smooth seed peas, to the stigma of a rough seed pea. Then the pollen from a rough seed pea, to the stigma of a smooth seed pea. For each of the seven paired traits. And he characterized and counted. Hundreds of pea plants, then thousands, then tens of thousands. For eight years.
Mendel’s peas tell a story about heredity
As the data from Mendel’s crosses slowly accumulated, he noticed things about the hybrids even before he had crunched the numbers. For example, he noted quite early that only one of the characteristics from one of the parents was displayed per offspring (either green or yellow seeds, but never both in the same plant). Furthermore, in the first generation of a cross, all of the offspring had the trait of one parent, never both. These results immediately contradicted the reigning hypothesis of blended traits from both parents.
As Mendel continued his experiments, he added crosses between the offspring to generate 2nd generation hybrids. In these offspring, Mendel found that the missing trait from the other parent suddenly re-appeared. An interesting and most important fact did not appear until he carefully reviewed and analyzed the mass of data: that the missing trait re-appeared in a ratio of about 1:3 with the greater portion being the single trait of the 1st generation. His observations and this numerical ratio of traits were essential to his insights. Mendel called the more common trait the dominant trait, and the less common one the recessive trait.
Mendel began to form an amazing insight and belatedly a world-shaking set of principles of inheritance. He hypothesized that an offspring receives a particle or factor of inheritance from each parent accounting for the parent’s traits. An individual receiving a dominant factor will always show that trait preferentially over a recessive one. If the offspring receives two recessive particles of inheritance, then the recessive trait will finally appear in that individual. This hypothesis became known as the Law of Segregation (each parent passes a factor – now called an allele – to its offspring). In order for this to occur, Mendel further hypothesized that during the formation of sex cells, the gametes, the factors of inheritance, each segregates independently into two separate sex cells. This became known as the Law of Independent Assortment (the two alleles for each trait are passed into gametes independently of each other). Remember, this was long before anyone had even seen chromosomes in the nucleus of cells, or knew that they come in pairs (one from each parent), or that they contained genes that control the production of proteins which are responsible for many of the traits we can see and many we can't.
Mendel presented his paper, Experiments on Plant Hybridization, at the Natural History Society of Brno early in 1865. This paper should have shaken the world at that very moment in time. But it was not to be. Those in the audience, several dozen, appear to have failed to understand its significance. Charles Darwin’s book On the Origin of Species was published a few years before on November 24, 1859. Mendel’s work would have provided an invaluable mechanistic explanation for Darwin’s theories, and would have been embraced immediately by him. Darwin’s much more influential social position in Victorian England could have given Mendel’s work an invaluable boost of publicity and his stamp of approval. Instead, Mendel’s papers were ignored and forgotten for almost four decades, until around 1900 when Hugo DeVries and Carl Correns independently duplicated his work, only then to rediscover Mendel’s papers and laws. After 1900, many biologists finally started to acknowledge Mendel’s work, replicated his data, and rapidly extended this new field of genetics.
Mendel’s quiet end
Mendel was elected abbot in 1868, shortly after his papers were published, and was immediately consumed by administrative duties which effectively ended his scientific work. Although he tried to keep active in areas such as meteorology and botany and beekeeping, his energies were ultimately harnessed to things like opposing an 1874 tax law which targeted his monastery. Although by this time it was clear that his paper was having no effect on the scientific community, Mendel reportedly told a friend, “My time will come”.
Mendel died January 6, 1884 at the age of 61 and was buried in the monastery where he worked and lived, his life’s work still unknown. But as he told his friend, his time eventually came and the world now acknowledges Mendel as the Father of Genetics.
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