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|Gregor Johann Mendel
founder of genetics
Gregor Johann Mendel was born of peasant parents in Heizendorf, then in the Austro-Hungarian Empire (now Hynice, Czech Republic), on July 20, 1822 (according to his baptismal certificate, but his family celebrated his birthday on July 22). He received his early education under the tutelage of Paster Schreiber, who recognized his pupil's abilities and convinced his family to send him away for further schooling. He continued his education at Leipnik, then at the district Gymnasium at Troppau, distinguishing himself at both schools. In 1838, Gregor's father was seriously injured in a farm accident and left unable to farm. Left without finances, Mendel took the course for school candidates and private teachers and then began to earn a meager living by private tutoring. He graduated from the Gymansium in 1840.
Mendel wanted to attend the Philosophical Institute at Olmütz, but since he lacked influential friends who could get him work as a tutor he was unable to obtain the necessary funds. The disappointment left him physically ill, and he spent a year with his parents. Returning to Olmütz in 1841, he was able to obtain just enough work to meet his minimal expenses. His younger sister, Theresa, gave her dowry for his education. Gregor later repaid the generous gift by educating her three sons, two of whom became physicians.
In 1843, Mendel entered the Augustinian monastery of St. Thomas at Brünn, Austria (now Brno, Czech Republic). He was ordained on August 6, 1847, and soon after was assigned to teach Greek and mathematics at the Gymnasium in Znaim; he only served one year, however, because he lacked the credentials for a permanent appointment. In 1850, he took the examination for his permanent teaching credentials. Although he failed the exam, one examiner was impressed enough to persuade the abbot to send him to the University of Vienna (1851-1853), where he studied physics, chemistry, mathematics, zoology, botany, and microscopy. In May 1856, he again took the examination, and again he failed. He never took the test again, and retained the title of substitute teacher at the Brünn Modern School for the next fourteen years.
Experiments in Heredity
It was at the monastery that Mendel conducted the experiments for which is best remembered. His keen interest in the natural sciences led him to try and determine how physical traits were passed from one generation to the next. Although other scientists were conducting research into heredity at the time, Mendel came up with a completely different method. His contemporaries were using plants and animals that differed in numerous characteristics and were, therefore, unable to get consistent results. Mendel decided it would be better to focus on individual characteristics within a single plant species.
In 1856, Mendel obtained pairs of different varieties of pure-breeding yellow peas (Pisum sativum), each pair differing in one easily diagnosed trait -- seed color (yellow or green), seed shape (smooth or wrinkled), pod color (yellow or green), pod shape (inflated or pinched), flower color (purple or white), flower position (axial or terminal), or stem height (tall or short). After two years of growing different varities to make sure the offspring was always the same, he began breeding different varieties together to make hybrids -- brushing the pollen off yellow pea plants and putting it on green pea plants (etc). For more than eight years he grew generation after generation of hybrids and tracked the inheritance of the traits.
Generation One Mendel began by breeding two different plants -- one tall and one dwarf, for example -- with each other. This produced a generation of nothing but tall plants. (According to the prevailing theory of the day, Mendel should have ended up with a bed of pea plants that were somewhere between tall and dwarf in height.)
To explain his results, Mendel conceived of hereditary units, now called genes, which often expressed dominant or recessive characteristics. According to his Law of Segregation, genes normally occur in pairs in the ordinary body cells, but segregate in the formation of gametes (eggs or sperm), each member of the pair becoming part of the separate sex cell. When egg and sperm unite, forming a gene pair, the dominant gene (tallness, for example) masks the recessive gene (dwarfness).
Generation Two Mendel then bred the hybrid offspring of the first generation with each other. The result was a generation of both tall and dwarf plants, in a ratio of three tall to one dwarf.
To explain this result, Mendel correctly determined that the genes paired into AA, Aa, and aa ("A" representing dominant and "a" recessive).
Generation Three Breeding dwarf plants from the second generation with each other always produced a generation of dwarf plants. One third of the tall offspring bred true, while the other two thirds produced offspring in a ratio of three tall to one dwarf. The same results were obtained for all seven pairs of traits, in all three generations.
From the third generation, Mendel determined that the hereditary units did not blend, as his predecessors believed, but remained unchanged from one generation to another. He thus formulated the Law of Independent Assortment, in which the expression of a gene for any single characteristic is usually not influenced by the expression of another characteristic.
Mendel reported his experiments to the Brünn Natural Science Society in the spring of 1865; his paper, Treatises on Plant Hybrids, was published in the proceedings of the society the next year. Despite, or possibly because of, the magnitude of Mendel's work, no questions were asked during his presentation, and his paper went largely ignored by the scientific community.
Mendel's later experiments with the hawkweed (Hieracium) proved inconclusive. In 1868, his fellow monks unanimously elected him abbot, and by the 1870s the duties of his office had forced him to give up his experiments. His final years were spent in a dispute over taxation. Believing that an 1874 law taxing monasteries was unconstitutional, Mendel refused to pay the tax, which resulted in sanctions being levied against the monastery. The case was not settled until after his death. He died of Bright's Disease on January 6, 1884.
Recognition of His Work
Mendel's work remained virtually unknown until 1900. Then, three men -- Hugo de Vries of the Netherlands, Carl Correns of Germany, Erich von Tschermak of Austria -- independently did similar experiments and derived the same conclusions as Mendel had. But it wasn't until they searched the literature that they realized that Mendel had anticipated them by thirty-five years. Today, geneticists still refer to genes as being either dominant or recessive, and both of his laws are still taught to students of the natural sciences.
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