Asexual Reproduction
Asexual reproduction is reproduction by a single parent that produces offspring genetically identical to itself, with no fusion of gametes.
Definition
Asexual reproduction is when one parent makes a new living thing all by itself, without a mate, and the offspring is an exact copy of the parent. It involves a single parent and no gametes, producing genetically identical offspring (clones) by methods such as binary fission in bacteria, budding in yeast and hydra, fragmentation and regeneration in starfish and some worms, spore formation in fungi, and vegetative reproduction in plants, with mitosis as the underlying process in eukaryotes. Other routes include parthenogenesis (development from an unfertilized egg) and apomixis in plants, all without meiosis or syngamy. Genetic variation arises only through mutation, so populations are genetically uniform and vulnerable to pathogens and environmental change, but the strategy avoids the twofold cost of sex, since no males are needed, and keeps well-adapted genotypes intact. Many organisms alternate between asexual reproduction under favorable conditions and sexual reproduction under stress.
Example
A strawberry plant sends out runners that grow into new plants, a bacterium splits in two, and a starfish can grow a whole new body from one arm. A bacterium dividing every $30$ minutes produces $2^{48}$, about $2.8 \times 10^{14}$, descendants in $24$ hours if nothing limits growth, every one carrying the same DNA as the first cell apart from rare mutations. Aphids reproduce by parthenogenesis all summer, with females giving live birth to identical daughters that are already carrying developing embryos, then switch to sexual reproduction in autumn to produce hardy eggs, and whiptail lizards of the genus Aspidoscelis include species that are entirely female and reproduce only by parthenogenesis.
Key Insight
Asexual reproduction is fast and easy, but every offspring is the same, so if a disease can kill one it can kill them all. Its advantage is speed and certainty and its disadvantage is no variation, which makes it work best in stable environments where the parent's traits are already a good fit. Asexual lineages can dominate in the short term but rarely persist over evolutionary time, because without recombination they cannot purge harmful mutations or assemble beneficial ones; the bdelloid rotifers, apparently asexual for tens of millions of years, are the famous exception biologists still study.