How does mutation, random fertilization, and crossing over contribute to genetic variation?

Mutation are two types somatic and germ cell mutation...as there is mutation in germ cell it will alter the normal behavior and produce variation !

random fertilization also causes variation as different setup of genes meets with another different...so chances of variation increases !

and third crossing over is in meiosis when chiasmata formsso in this two homologous chromosome attach to each other and on separation ... some part exchange so leads to variation !