Monoploid organisms reproduce asexually since they need to transmit all of their genetic material to their offspring. Diploid organisms, have 2 copies of their genetic material that differ slightly in their genes. Since the progeny gets half of the DNA from each parent, we have that new combinations can emerge; for example, if the mother is AA for some allele and the father aa, their offspring will be Aa, a new genotype. This might have different implications (for example, the recessive gene for thalassemia also provides resistance to malaria). Finally, during meiosis, there is also an event called crossover that increases the genetic variation of the offspring.
