| Popis: |
This chapter emphasizes fungal genetics and evolution. Three concepts for population genetics are individual, population, and species. The sexual process in fungi involves three key steps: cell fusion, nuclear fusion and meiosis. The five basic types of life cycle in fungi are haploid, haploid-dikaryotic, haploid–diploid, diploid, and asexual process. The sexual process occurs only if two strains that differ in mating type interact, as in breeding systems with two mating types, unifactorial incompatibility systems with many mating types, and bifactorial incompatibility systems. Self-fertile species occur in all major groups of fungi. This chapter also discusses sexual differentiation, and its roles and relationship to outcrossing. There are many fungi in which the sexual process has not been observed, including about 14,000 mitosporic species—about 20% of all known fungi. Gene mutation is the source of genetic variability. The transfer of genes between populations that are spatially separated and less likely to exchange genes is termed gene flow. Microevolution refers to small genetic changes in populations that are usually reversible with sufficient speed to be accessible to observation and experiment. Microevolution takes the form of changes in the frequency of alleles. Factors bringing about microevolution are mutation pressure, gene flow, natural selection, random genetic drift, and the founder effect and molecular drive. The close resemblance between successive species implies speciation—the origin of a new species from a pre-existing species. Traditional classification of diversity includes natural and artificial. The correct identification of fungi is important in plant pathology, medical and veterinary mycology, biodeterioration, biotechnology, and environmental studies. |
