Regardless, the "re-discovery" made Mendelism an important but controversial theory. Later scholars have accused Von Tschermak of not truly understanding the results at all. De Vries may not have acknowledged truthfully how much of his knowledge of the laws came from his own work and how much came only after reading Mendel's paper. The exact nature of the "re-discovery" has been debated: De Vries published first on the subject, mentioning Mendel in a footnote, while Correns pointed out Mendel's priority after having read De Vries' paper and realizing that he himself did not have priority. In 1900, however, his work was "re-discovered" by three European scientists, Hugo de Vries, Carl Correns, and Erich von Tschermak. A major roadblock to understanding their significance was the importance attached by 19th-century biologists to the apparent blending of many inherited traits in the overall appearance of the progeny, now known to be due to multi-gene interactions, in contrast to the organ-specific binary characters studied by Mendel. Although they were not completely unknown to biologists of the time, they were not seen as generally applicable, even by Mendel himself, who thought they only applied to certain categories of species or traits. Mendel's results were at first largely ignored. He described his experiments in a two-part paper, Versuche über Pflanzen-Hybriden ( Experiments on Plant Hybridization), that he presented to the Natural History Society of Brno on 8 February and 8 March 1865, and which was published in 1866. From these experiments, he induced two generalizations which later became known as Mendel's Principles of Heredity or Mendelian inheritance. Between 18, Mendel cultivated and tested some 5,000 pea plants. This model was used to work out how genes code for proteins.The principles of Mendelian inheritance were named for and first derived by Gregor Johann Mendel, a nineteenth-century Moravian monk who formulated his ideas after conducting simple hybridisation experiments with pea plants ( Pisum sativum) he had planted in the garden of his monastery. They showed that bases occurred in pairs, and X-ray data showed that there were two strands coiled into a double helix. By using data from other scientists Rosalind Franklin and Maurice Wilkins, they were able to build a model of DNA. In the mid-20 th century two scientists, James Watson and Francis Crick worked out the structure of DNA. This led to the theory that the 'units', now called genes, were located on chromosomes. In the early 20 th century, it was observed that chromosomes and Mendel's 'units' behaved in similar ways. The idea that genes were located on chromosomes emerged in the late 19 th century when better microscopes and staining techniques allowed the visualisation and behaviour of chromosomes during cell division.
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