A single-cell diploid organism acquires a deleterious point mutation before entering mitosis. If one of the daughter cells reproduces asexually, and the other daughter cell goes through meiosis to produce gametes that fuse with gametes from other individuals. The daughter cell undergoing meiosis will be the most evolutionarily successful. In the process of meiosis the DNA gets crossed between two organisms leading to an offspring without any deleterious point mutation. In case of asexual reproduction, the daughter cell will give an identical set of genome to its offspring. Hence the offspring will also carry the mutation, and depending on the lethality of the mutation the lineage will propagate.