tailieunhanh - Encyclopedia of Global Resources part 55

Encyclopedia of Global Resources part 55 provides a wide variety of perspectives on both traditional and more recent views of Earth's resources. It serves as a bridge connecting the domains of resource exploitation, environmentalism, geology, and biology, and it explains their interrelationships in terms that students and other nonspecialists can understand. The articles in this set are extremely diverse, with articles covering soil, fisheries, forests, aluminum, the Industrial Revolution, the . Department of the Interior, the hydrologic cycle, glass, and placer mineral deposits. . | 488 Genetic diversity Global Resources Genetic diversity Category Ecological resources Genetic diversity includes the inherited traits encoded in the deoxyribonucleic acid DNA of all living organisms and can be examined on four levels among species among populations within populations and within individuals. Populations with higher levels of diversity are better able to adapt to changes in the environment are more resistant to the deleterious effects of inbreeding and provide more opportunities for animal and plant breeders to cultivate types or varieties with qualities desired by humans. Background Genetic diversity is the most fundamental level of biological diversity because genetic material is responsible for the variety of life. For new species to form genetic material must change. Changes in the inherited properties of populations occur deterministically through gene flow mating between individual organisms representing formerly separated populations and through natural or artificial selection which occurs when some types of individuals breed more successfully than others . Change can also occur randomly through mutations or genetic drift when the relative proportions of genes change by chance in small populations . Populations with higher levels of diversity tend to do better to have more survival options as surroundings change than do populations particularly smaller ones with lower levels of genetic diversity. Preservation Efforts Conservation efforts directed at maintaining genetic diversity involve both germ plasm preservation germ plasm kept in a steady state for periods of time and germ plasm conser vation germ plasm kept in a natural evolving state . The former usually involves ex situ laboratory techniques in which genetic resources are removed from their natural habitats. They include seminatural strategies such as botanical gardens arboretums nurseries zoos farms aquariums and captive fisheries as well as completely artificial methods such as seed