Sexual vs Asexual Reproduction

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Asexual reproduction involves one parent and produces genetically identical offspring (clones) by mitosis: binary fission, budding, runners, spores. It is fast and needs no mate, but lacks variation. Sexual reproduction involves the fusion of male and female gametes, producing genetically different offspring.

Gametes are made by meiosis, which halves the chromosome number so that fertilisation restores the full set. Variation arises from independent assortment of chromosomes, crossing over and random fertilisation. This variation helps a species survive changing conditions and disease, which is why it is favoured in unstable environments.

Asexual reproduction suits stable environments. A strawberry plant sends out runners that root into new plants, bacteria split every twenty minutes, and yeast buds. A single aphid can produce many genetically identical offspring without mating. Some organisms, like Plasmodium and many fungi, use both methods at different times.

Gardeners use cuttings to keep a desirable plant exactly the same. A downside is that if a disease suits one clone, all can be wiped out, as with the banana variety Gros Michel. A common error is thinking clones are different in any way; they are identical unless a mutation occurs.