Gregor Mendel

Gregor Johann Mendel (Czech: Řehoř Jan Mendel; 20 July 1822 – 6 January 1884) (English /ˈmɛndəl/) was a scientist, Augustinian friar and abbot of St. Thomas' Abbey in Brno, Margraviate of Moravia. Mendel was born in a German-speaking family in Silesian part of Austrian Empire (today's Czech Republic) and gained posthumous recognition as the founder of the modern science of genetics. Though farmers had known for centuries that crossbreeding of animals and plants could favor certain desirable traits, Mendel's pea plant experiments conducted between 1856 and 1863 established many of the rules of heredity, now referred to as the laws of Mendelian inheritance.
Mendel worked with seven characteristics of pea plants: plant height, pod shape and color, seed shape and color, and flower position and color. With seed color, he showed that when a yellow pea and a green pea were bred together their offspring plant was always yellow. However, in the next generation of plants, the green peas reappeared at a ratio of 1:3. To explain this phenomenon, Mendel coined the terms “recessive” and “dominant” in reference to certain traits. (In the preceding example, green peas are recessive and yellow peas are dominant.) He published his work in 1866, demonstrating the actions of invisible “factors”—now called genes—in providing for visible traits in predictable ways.
The profound significance of Mendel's work was not recognized until the turn of the 20th century (more than three decades later) with the independent rediscovery of these laws. Erich von Tschermak, Hugo de Vries, Carl Correns, and William Jasper Spillman independently verified several of Mendel's experimental findings, ushering in the modern age of genetics.

Mendel was born into an Austrian family of German descent in Hynčice, Moravian-Silesian border, Austrian Empire (now Hynčice, Czech Republic). He was the son of Anton and Rosine (Schwirtlich) Mendel, and had one older sister, Veronika, and one younger, Theresia. They lived and worked on a farm which had been owned by the Mendel family for at least 130 years. During his childhood, Mendel worked as a gardener and studied beekeeping. Later, as a young man, he attended gymnasium in Opava (called Troppau in German). He had to take four months off during his gymnasium studies due to illness. From 1840 to 1843, he studied practical and theoretical philosophy and physics at the Philosophical Institute of the University of Olomouc, taking another year off because of illness. He also struggled financially to pay for his studies, and Theresia gave him her dowry. Later he helped support her three sons, two of whom became doctors.

He became a friar because it enabled him to obtain an education without having to pay for it himself. He was given the name Gregor (Řehoř in Czech) when he joined the Augustinian friars.

When Mendel entered the Faculty of Philosophy, the Department of Natural History and Agriculture was headed by Johann Karl Nestler who conducted extensive research of hereditary traits of plants and animals, especially sheep. Upon recommendation of his physics teacher Friedrich Franz, Mendel entered the Augustinian St Thomas's Abbey in Brno (called Brünn in German) and began his training as a priest. Born Johann Mendel, he took the name Gregor upon entering religious life. Mendel worked as a substitute high school teacher. In 1850, he failed the oral part, the last of three parts, of his exams to become a certified high school teacher. In 1851, he was sent to the University of Vienna to study under the sponsorship of Abbot C. F. Napp so that he could get more formal education. At Vienna, his professor of physics was Christian Doppler. Mendel returned to his abbey in 1853 as a teacher, principally of physics. In 1856, he took the exam to become a certified teacher and again failed the oral part. In 1867, he replaced Napp as abbot of the monastery.

After he was elevated as abbot in 1868, his scientific work largely ended, as Mendel became consumed with his increased administrative responsibilities, especially a dispute with the civil government over their attempt to impose special taxes on religious institutions. Mendel died on 6 January 1884, at the age of 61, in Brno, Moravia, Austria-Hungary (now Czech Republic), from chronic nephritis. Czech composer Leoš Janáček played the organ at his funeral. After his death, the succeeding abbot burned all papers in Mendel's collection, to mark an end to the disputes over taxation.

Experiments on plant hybridization

Dominant and recessive phenotypes. (1) Parental generation. (2) F1 generation. (3) F2 generation.

Gregor Mendel, who is known as the "father of modern genetics", was inspired by both his professors at the Palacký University, Olomouc, (Friedrich Franz and Johann Karl Nestler) and his colleagues at the monastery (such as Franz Diebl) to study variation in plants. In 1854, Napp authorized Mendel for the investigation, who conducted his study in the monastery's 2 hectares (4.9 acres) experimental garden, which was originally planted by Napp in 1830. Unlike Nestler, who studied hereditary traits in sheep, Mendel focused on plants. After initial experiments with pea plants, Mendel settled on studying seven traits that seemed to inherit independently of other traits: seed shape, flower color, seed coat tint, pod shape, unripe pod color, flower location, and plant height. He first focused on seed shape, which was either angular or round. Between 1856 and 1863 Mendel cultivated and tested some 28,000 plants, majority of which were pea plants (Pisum sativum). This study showed that one in four pea plants had purebred recessive traits, two out of four were hybrid and one out of four were purebred dominant. His experiments led him to make two generalizations, the Law of Segregation and the Law of Independent Assortment, which later came to be known as Mendel's Laws of Inheritance.

Mendel presented his paper, "Versuche über Pflanzenhybriden" ("Experiments on Plant Hybridization"), at two meetings of the Natural History Society of Brno in Moravia on 8 February and 8 March 1865. It was received favorably and generated reports in several local newspapers. When Mendel's paper was published in 1866 in Verhandlungen des naturforschenden Vereins Brünn, it was seen as essentially about hybridization rather than inheritance and had little impact and was cited about three times over the next thirty-five years. His paper was criticized at the time, but is now considered a seminal work. Notably, Charles Darwin was unaware of Mendel's paper, and it is envisaged that if he had, genetics would have been a much older science.

Other experiments

Mendel began his studies on heredity using mice. He was at St. Thomas's Abbey but his bishop did not like one of his friars studying animal sex, so Mendel switched to plants. Mendel also bred bees in a bee house that was built for him, using bee hives that he designed. He also studied astronomy and meteorology, founding the 'Austrian Meteorological Society' in 1865. The majority of his published works were related to meteorology.

Mendel also experimented with hawkweed and honeybees. However, none of his results on these survived, except for passing mention in the reports of Moravian Apiculture Society. All that is known definitely is that he used Cyprian and Carniolan bees, which were particularly aggressive to the annoyance of other monks and visitors of the monastery such that he was asked to get rid of them. In contrast, he had a fondness for the bees, and refer to them as "my dearest little animals".

He also described novel plant species, and these are denoted with the botanical author abbreviation "Mendel".

Mendel's work was rejected at first in the scientific community, and was not widely accepted until after he died. During his own lifetime, most biologists held the idea that all characteristics were passed to the next generation through blending inheritance, in which the traits from each parent are averaged together. Instances of this phenomenon are now explained by the action of multiple genes with quantitative effects. Charles Darwin tried unsuccessfully to explain inheritance through a theory of pangenesis. It was not until the early twentieth century that the importance of Mendel's ideas was realized.

By 1900, research aimed at finding a successful theory of discontinuous inheritance rather than blending inheritance led to independent duplication of his work by Hugo de Vries and Carl Correns, and the rediscovery of Mendel's writings and laws. Both acknowledged Mendel's priority, and it is thought probable that de Vries did not understand the results he had found until after reading Mendel. Though Erich von Tschermak was originally also credited with rediscovery, this is no longer accepted because he did not understand Mendel's laws. Though de Vries later lost interest in Mendelism, other biologists started to establish genetics as a science. All three of these researchers, each from a different country, published their work rediscovering Mendel's work within a two-month span in the Spring of 1900.

Mendel's results were quickly replicated, and genetic linkage quickly worked out. Biologists flocked to the theory; even though it was not yet applicable to many phenomena, it sought to give a genotypic understanding of heredity which they felt was lacking in previous studies of heredity which focused on phenotypic approaches. Most prominent of these previous approaches was the biometric school of Karl Pearson and W. F. R. Weldon, which was based heavily on statistical studies of phenotype variation. The strongest opposition to this school came from William Bateson, who perhaps did the most in the early days of publicising the benefits of Mendel's theory (the word "genetics", and much of the discipline's other terminology, originated with Bateson). This debate between the biometricians and the Mendelians was extremely vigorous in the first two decades of the twentieth century, with the biometricians claiming statistical and mathematical rigor, whereas the Mendelians claimed a better understanding of biology. (Modern genetics shows that Mendelian heredity is in fact an inherently biological process, though not all genes of Mendel's experiments are yet understood.)

In the end, the two approaches were combined, especially by work conducted by R. A. Fisher as early as 1918. The combination, in the 1930s and 1940s, of Mendelian genetics with Darwin's theory of natural selection resulted in the modern synthesis of evolutionary biology.

Mendel's experimental results have later been the object of considerable dispute. Mendel used crosses between true-breeding (homozygous) pea plants for each of the seven traits. In each case the offspring (F1) would be heterozygous and would therefore display the dominant state uniformly (such as round or green peas). In 1936, R.A. Fisher reconstructed Mendel's experiments, analyzed results from the F2 (second filial) generation and found the ratio of dominant to recessive phenotypes (e.g. green versus yellow peas; round versus wrinkled peas) to be implausibly close to the expected ratio of 3 to 1. Mendel allowed pea plants showing the dominant phenotype to self-fertilize in order to determine the ratio of homozygotes to heterozygotes from the occurrence of recessive phenotype progeny. Fisher was sceptical of Mendel's 1:2 ratio of true-breeding (homozygotes) to mixed progeny (heterozygotes), and said Mendel's results were "Too good to be true." In particular, Fisher suggested that Mendel inferred parental phenotype by examination of 10 progeny, but did not adjust his expectation for the probability that a heterozygote parent could produce 10 dominant phenotype offspring (this occurs with a frequency of 0.7510 = 6% of tests). Thus corrected one should expect a ratio of 1.7:1, quite different from Mendel's results of 720:353, which are an extremely close fit to Mendel's incorrect expectation of 2:1. This statistical interpretation was taken as the ground for criticising Mendel's works as a whole, in 1998 amounting to an accusation of experimental fraud by removing outliers, "tidying" datasets and repeating experiments. Fisher asserted, that "the data of most, if not all, of the experiments have been falsified so as to agree closely with Mendel's expectations," and he called Mendel's result "abominable", "shocking", and "cooked".

Fisher accused Mendel's experiments as "biased strongly in the direction of agreement with expectation... to give the theory the benefit of doubt". This has been often cited as an example of confirmation bias. This might arise if he detected an approximate 3 to 1 ratio early in his experiments with a small sample size, and, in cases where the ratio appeared to deviate slightly from this, continued collecting more data until the results conformed more nearly to an exact ratio. In his 2004, J.W. Porteous concluded that Mendel's observations were implausible. However, reproduction of the experiments has demonstrated that there is no real bias towards Mendel's data. In 2007, Daniel L. Hartl and Daniel J. Fairbanks suggested that Fisher incorrectly interpreted these experiments. They found it likely that Mendel scored more than 10 progeny, and that the results matched the expectation. They conclude, "Fisher's allegation of deliberate falsification can finally be put to rest, because on closer analysis it has proved to be unsupported by convincing evidence." In 2008 Hartl and Fairbanks (with Allan Franklin and AWF Edwards) wrote a comprehensive book in which they concluded that there were no reasons to assert Mendel fabricated his results, nor that Fisher deliberately tried to diminish Mendel's legacy. Reassessment of the statistical analyses also disprove the notion of confirmation bias in Mendel's results.