Because of the following factors, sexual reproduction leads to numerous viable variations:
(a) A mistake in DNA copying (though it was rare)
At the moment sex cells develop, paternal and maternal chromosomes are randomly segregated.
(c) When gametes are formed, homologous chromosomes exchange genetic material.
(d) Variations accumulated as a result of reproduction over many generations, and extensive diversity was naturally produced by choice.
(e) Because there is only one parent engaged in asexual reproduction, variation is highly constrained. As a result, the offspring shares the parent’s genetic makeup.