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Being overweight and having high blood pressure can independently increase a man’s chances of developing kidney cancer, according to a new study. |
Genetics |
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Some of the differences and similarities between parents and offspring recur from generation to generation in repeated patterns. The investigation of these patterns has led to some of the most exciting discoveries in modern biology. The science of genetics began in 1900. The first observation of genetics can be attributed to the work of the Austrian monk Gregor Mendel, which was published in 1866 but was virtually ignored. Mendel presented his observation on working with garden peas. Mendel described the patterns of inheritance in terms of seven pairs of contrasting traits that appeared in different pea plant varieties. He observed that the traits were inherited as separate units, each of which was inherited independently of the others. His observation was that each parent has a pair of unit but contributed only one unit from the pair to its offspring. This unit was later given the name Genes. Mendel discovered that by crossing tall and dwarf parents, for example, he got hybrid offspring that resembled the tall parent rather than being a medium-height blend. To expain this he conceived of the hereditary units which are now called genes. These hereditary units often expressed dominant or recessive characteristics. Formulating his first principle (the law of segregation), Mendel stated that genes normally occur in pairs in the ordinary body cells, but segregate in the formation of sex cells (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) masks the recessive gene (shortness). On interbreeding the first hybrid tall peas Mendel found that the second generation turned out in a ratio of three tall to each short offspring. He formulated that the genes paired into AA, Aa, and aa ("A" representing dominant and "a" representing recessive). He found that the self-pollinated AA bred true to produce pure tall plants, that the aa plant produced pure dwarf plants, and that the Aa, or hybrid, tall plants produced the same three-to-one ratio of offspring. From this Mendel observed that the hereditary units did not blend and remained unchanged from one generation to the next. Thus his second principle was - the law of independent assortment -- the expression of a gene for any single characteristic is usually not influenced by the expression of another characteristic. The Medel's Laws became the basis for modern genetics. |
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