July 20, 2010 <Back to Index>
|
Gregor Johann Mendel (July 20, 1822 – January 6, 1884) was an Augustinian priest and scientist, who gained posthumous fame as the figurehead of the new science of genetics for his study of the inheritance of certain traits in pea plants. Mendel showed that the inheritance of these traits follows particular laws, which were later named after him. The significance of Mendel's work was not recognized until the turn of the 20th century. The independent rediscovery of these laws formed the foundation of the modern science of genetics. Mendel was born into an ethnic German family in Heinzendorf bei Odrau, Austrian Silesia, Austrian Empire (now Hynčice, Czech Republic), and was baptized two days later. He was the son of Anton and Rosine
Mendel, and had one older sister and one younger. 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, studied beekeeping, and as a young man attended the Philosophical Institute in Olomouc in 1840–1843. Upon recommendation of his physics teacher Friedrich Franz, he entered the Augustinian Abbey of St Thomas in Brno in 1843. Born Johann Mendel, he took the name Gregor upon entering monastic life. In 1851 he was sent to the University of Vienna to study under the sponsorship of Abbot C.F. Napp. At Vienna, his professor of physics was Christian Doppler. Mendel
returned to his abbey in 1853 as a teacher, principally of physics, and
by 1867, he had replaced Napp as abbot of the monastery. Besides
his work on plant breeding while at St Thomas's Abbey, 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. Gregor
Mendel, who is known as the "father of modern genetics", was inspired
by both his professors at university and his colleagues at the
monastery to study variation in plants, and he conducted his study in
the monastery's two hectare experimental garden, which was originally planted by the abbot Napp in 1830. Between 1856 and 1863 Mendel cultivated and tested some 29,000 pea plants (i.e., Pisum sativum). This study showed that one in four pea plants had purebred recessive alleles, two out of four were hybrid and one out of four were purebred dominant. His experiments brought forth two generalizations, the Law of Segregation and the Law of Independent Assortment, which later became known as Mendel's Laws of Inheritance. Mendel did read his paper, Experiments on Plant Hybridization, at two meetings of the Natural History Society of Brünnin Moravia in 1865. When Mendel's paper was published in 1866 in Proceedings of the Natural History Society of Brünn, it had little impact and was cited about three times over the next thirty-five years. (Notably, Charles Darwin was unaware of Mendel's paper, according to Jacob Bronowski's The Ascent of Man.) His paper was criticized at the time, but is now considered a seminal work. After
Mendel completed his work with peas, he turned to experimenting with
honeybees, in order to extend his work to animals. He produced a hybrid
strain (so vicious they were destroyed), but failed to generate a clear
picture of their heredity because of the difficulties in controlling
mating behaviours of queen bees. He also described novel plant species, and these are denoted with the botanical author abbreviation "Mendel". 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. At
first Mendel's work was rejected, and it was not widely accepted until
after he died. At that time most biologists held the idea of blending inheritance, and Charles Darwin's efforts to explain inheritance through a theory of pangenesis were unsuccessful. Mendel's ideas were rediscovered in the early twentieth century, and in the 1930s and 1940s the modern synthesis combined Mendelian genetics with Darwin's theory of natural selection. Mendel died on January 6, 1884, at age 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. It
was not until the early 20th century that the importance of his 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. 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 latter 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. In
the end, the two approaches were combined as the modern synthesis of evolutionary biology, especially by work conducted by R.A. Fisher as early as 1918. Mendel's experimental results have later been the object of considerable dispute. Fisher analyzed the results of the F2 (second filial) ratio and found them to be implausibly close to the exact ratio of 3 to 1. Only a few would accuse Mendel of scientific malpractice or call it a scientific fraud — reproduction
of his experiments has demonstrated the validity of his
hypothesis — however, the results have continued to be a mystery for
many, though it is 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 continued collecting more
data until the results conformed more nearly to an exact ratio. It is
sometimes suggested that he may have censored his results, and that his
seven traits each occur on a separate chromosome pair, an extremely
unlikely occurrence if they were chosen at random. In fact, the genes
Mendel studied occurred in only four linkage groups, and only one gene
pair (out of 21 possible) is close enough to show deviation from independent assortment;
this is not a pair that Mendel studied. Some recent researchers have
suggested that Fisher's criticisms of Mendel's work may have been
exaggerated. |