Genetic Evolutionary Processes in Crepis

The primary genetic processes causing evolution in Crepis are gene mutations and structural changes in the chromosomes. 2. The roles of gene mutations are the production of morphological and physiological differentiation within and between species, the accumulation of intra- and interspecific sterility, and possibly the reduction in absolute size of the chromosomes. 3. The roles of chromosome changes are the genesis of intraspecific sterility leading to discontinuity and hence to speciation, and karyotype evolution through reduction in number and symmetry of the chromosomes. 4. The secondary genetic processes involved in the evolution of Crepis are interspecific hybridization, polyploidy and apomixis. 5. The roles of interspecific hybridization are the origin of a small number of new species, especially through amphidiploidy (cf. Babcock and Stebbins, 1938; Stebbins and Babcock, 1939), and the augmentation of karyotype evolution. 6. The roles of polyploidy and apomixis are a small amount of speciation combined with extensive differentiation and geographic distribution (Babcock and Stebbins, op. cit.).