Solution:The causes for variation in the genetic material of progeny are both mutation and sexual reproduction. During sexual reproduction meiosis occurs in which crossing over takes place where exchange of chromosomal segments occurs and random mating of male and female gametes occurs.
That is why new variations generated during sexual reproduction. During asexual reproduction no meiosis and mating of gametes occurs so little changes may occur due to the mutation which occurs randomly and suddenly.
Epigenetic is the study of change in gene expression that does not involve change to the underlying DNA sequence. It is a change in phenotype with a change in genotype.