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Gregor Mendel kimdir?
Gregor Johann Mendel (d. 20 Temmuz 1822 – ö. 6 Ocak 1884) kalıtım biliminin babası olarak anılan Avusturyalı bilim adamı ve rahip.
Kalıtım biliminin öncüsü botanikçi, bitkiler üzerine yaptığı çalışmalarda, bir türün özelliklerinin kalıtım yoluyla sonraki kuşaklara aktarıldığını bulmuştur. Mendel'in öne sürdüğü ilkeler, 20. yüzyılın başlarında yapılan deneylerle doğrulandıktan sonra, kalıtım kuramının bütün canlılar için geçerliliği saptanarak, biyolojinin temel ilkelerinden biri haline gelmiştir.
Yaşamı
Küçük yaşlarda bahçe işleriyle uğraşmaya başlayan Mendel, üniversite öğreniminden sonra bir din adamı olarak Moravya'da yaşamını sürdürdü. Bu arada bitkiler üzerinde pek başarıya ulaşamayan bazı incelemelerde bulundu.
1854'te Brünn'e dönerek bir teknik lisede öğretmenlik yapmaya başladı. Daha önce de öğretmenlik sınavlarına girmiş ancak başarılı olamamıştı. 19. yy. ortalarında Darwin'in doğal ayıklanma kuramının yayıldığı sıralarda canlı bir türün özelliklerinin kendisini izleyen döllere nasıl aktarabildiği sorunu yeni bir yoğunlukla ortaya çıkmıştı.
Biyoloji bilginleri özellikle bitkibilimciler harcadıkları çabalara karşın bu sorunu aydınlatamıyorlardı. Daha sonraları genetiğin babası olarak kabul edilecek Mendel, aynı sorunla ilgili deneylere 1858’de başladı ve araştırmalarının ancak 8 yıl sonra sonuca ulaştırabildi. Başarısı, incelediği konuya elverişli olan yönteminden kaynaklandı. Mendel bir yandan farkların az ve son derece belirgin olduğu bitki çeşitlerini (dev ya da cüce, düz ya da kırışık bezelyeler) ayırmayı öte yandan aktarılan özelliklere göre sayısal ilişkileri araştırmada istatistiğin henüz yerleşmiş bir bilim dalı olmadığı bir dönemde istatistik yöntemini benimsemeyi bildi.
Bezelyelerle yaptığı deneylerde bitkinin uzun boylu ya da cüce, çiçeklerin ve yaprak koltuklarının renkli ya da renksiz, tohumlarının sarı ya da yeşil, düzgün ya da buruşuk olması gibi karşıt özelliklerden birini kuşaklar boyu taşıyan saf soylar elde etmeyi başardı. Ardından bunları kendi aralarında çaprazladı. Sonuçta gözle görülür ölçüde belirgin olan bu iki seçenekli özelliklerin saf soylar ile melez döllerde temel kalıtım birimleri aracılığıyla ortaya çıktığını ve her özellik için bir çift genin bulunduğunu öne sürdü.
Mendel tüm bunları basit istatistiklerle değerlendirdi. Bu Mendel yasalarının temel ilkesi melez döllerin üreme hücrelerinde yarısı anneden yarısı babadan alınmış kalıtım birimlerinin bulunmasıdır.
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Gregor Johann Mendel (July 20, 1822[1] – January 6, 1884) was an Austrian Augustinian friarscientist, who gained posthumous fame as the founder 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.
BiographyMendel was born into an ethnic German family in Heinzendorf bei Odrau, Austrian Silesia, Austrian Empire (now Hynčice, Czech Republic),was baptized two days later as Johann. He was the son of AntonRosine (Schwirtlich) Mendel,had one older sister (Veronica)one younger (Theresia). They livedworked on a farm which had been owned by the Mendel family for at least 130 years.[3] During his childhood, Mendel worked as a gardener, studied beekeeping,as a young man attended Gymnasium (school) in Opava. Later, from 1840 to 1843, he studied practicaltheoretical philosophy as well as physics at the University of Olomouc Faculty of Philosophy, taking a year off through illness. When Mendel entered the Faculty of Philosophy, the Department of Natural HistoryAgriculture was headed by Johann Karl Nestler, who conducted extensive research of hereditary traits of plantsanimals, especially sheep. In 1843 Mendel began his training as a priest. 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 religious 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.[4] Mendel returned to his abbey in 1853 as a teacher, principally of physics,by 1867, he had replaced Napp as abbot of the monastery.[5]
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.[6] He also studied astronomymeteorology,[5] founding the 'Austrian Meteorological Society' in 1865.[4] The majority of his published works were related to meteorology.[4]
Experiments on plant hybridizationGregor Mendel, who is known as the "father of modern genetics", was inspired by both his professors at the University of Olomouc (i.e. Friedrich Franz & Johann Karl Nestler)his colleagues at the monastery (i.e. Franz Diebl) to study variation in plants,he conducted his study in the monastery's two hectare[7] experimental garden, which was originally planted by the abbot Napp in 1830.[5] Between 18561863 Mendel cultivatedtested 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 hybridone out of four were purebred dominant. His experiments led him to make two generalizations, the Law of Segregationthe Law of Independent Assortment, which later became known as Mendel's Laws of Inheritance.
Mendel did read his paper, Versuche über Pflanzenhybriden (Experiments on Plant Hybridization), at two meetings of the Natural History Society of Brünn in Moravia in 1865. It was received favorablygenerated reports in several local newspapers.[8] When Mendel's paper was published in 1866 in Verhandlungen des naturforschenden Vereins Brünn,[9] it was seen as essentially about hybridization rather than inheritancehad little impactwas 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.
Life after the pea experimentsAfter 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,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.[10] At first Mendel's work was rejected,it was not widely accepted until after he died. At that time most biologists held the idea of blending inheritance,Charles Darwin's efforts to explain inheritance through a theory of pangenesis were unsuccessful. Mendel's ideas were rediscovered in the early twentieth century,in the 1930s1940s 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.[11]
Rediscovery of Mendel's work
Dominantrecessive phenotypes. (1) Parental generation. (2) F1 generation. (3) F2 generation.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 VriesCarl Correns,the rediscovery of Mendel's writingslaws. Both acknowledged Mendel's priority,it is thought probable that de Vries did not understand the results he had found until after reading Mendel.[2] Though Erich von Tschermak was originally also credited with rediscovery, this is no longer accepted because he did not understand Mendel's laws.[12] Though de Vries later lost interest in Mendelism, other biologists started to establish genetics as a science.[2]
Mendel's results were quickly replicated,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 PearsonW.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",much of the discipline's other terminology, originated with Bateson). This debate between the biometriciansthe Mendelians was extremely vigorous in the first two decades of the twentieth century, with the biometricians claiming statisticalmathematical 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.[11] Fisher analyzed the results of the F2 (second filial) ratiofound them to be implausibly close to the exact ratio of 3 to 1.[13] 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,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,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,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
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