how crossover probability and mutation probability is selected
Answers
Crossover and mutation perform two different roles. Crossover (like selection) is a convergence operation which is intended to pull the population towards a local minimum/maximum. In an interesting aside, crossover is not one of the original genetic operators; Holland's original thesis used only selection and probabilistic mutation.
Mutation is a divergence operation. It is intended to occasionally break one or more members of a population out of a local minimum/maximum space and potentially discover a better minimum/maximum space.
Since the end goal is to bring the population to convergence, selection/crossover happen more frequently (typically every generation). Mutation, being a divergence operation, should happen less frequently, and typically only effects a few members of a population (if any) in any given generation.