منابع مشابه
Natural selection at linked sites in humans.
Theoretical and empirical work indicates that patterns of neutral polymorphism can be affected by linked, selected mutations. Under background selection, deleterious mutations removed from a population by purifying selection cause a reduction in linked neutral diversity. Under genetic hitchhiking, the rise in frequency and fixation of beneficial mutations also reduces the level of linked neutra...
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The crucial step in the separation of two populations of a sexually reproducing species into two new species — speciation — is the acquisition of reproductive isolation between them. Such isolation ensures that they can evolve independently of each other, and so end up with radically different genotypes and phenotypes. This causes the biological world to be divided up into the discrete taxonomi...
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Nowadays one of the most important energy sources is natural gas. By depletion of oil reservoirs in the world, natural gas will emerge as the future energy source for human life. One of the major concerns of gas suppliers is being able to supply this source of energy the entire year. This concern intensifies during more consuming seasons of the year when the demand for natural gas increases, r...
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Mrs Munro, Chairman of a London Teaching Area Health Authority, argues vigorously that current medical training needs improvement. While investigative diagnosis, acute medicine and medical research are well served, the caring and preventative specialties are inadequately encouraged as is a sense of responsibility both to patients and to the health service as a whole. Surgeons, she adds, seem pa...
متن کاملNatural selection
The time-scale of evolution Think of the 3.5 billion years that makes the history of life on earth as stretching for a single year. On the first of January, there is nothing more than primitive bacteria, and this remains the case for the next eight months. Multicellular eukaryotic life appears in early September, vertebrates invade the land at the beginning of December and dinosaurs become exti...
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ژورنال
عنوان ژورنال: Science
سال: 1893
ISSN: 0036-8075,1095-9203
DOI: 10.1126/science.ns-21.524.94-a