Answer
In asexual reproduction, organisms want to clone themselves in a stable environment for which their genotype/phenotype is well adapted. They use only mitosis. When the environment is unstable, the genetic recombination which comes from crossing over and from assorting chromosomes into gametes is of benefit in generating genetic diversity on which natural selection can act to pick better adapted genotypes/phenotypes.
Work Step by Step
Review the chapter with an eye to details about mitosis and meiosis, and review the last several chapters to see more details about these. Combine this with the insights of this chapter about the role of linkage in genetics and the role of chromosomes in heredity.
