Reproduction is the biological process by which organisms produce new individuals. It is one of the defining characteristics of life — without reproduction, lineages end.
Asexual reproduction produces offspring that are genetically identical to the parent (clones). Bacteria divide by binary fission. Yeast buds. Hydra regenerates from fragments. Plants propagate vegetatively through runners, tubers, and cuttings. Asexual reproduction is fast, requires no mate, and efficiently copies a successful genotype. Its disadvantage is that offspring have no genetic variation beyond what mutation introduces — if the environment changes, the entire lineage may be equally vulnerable.
Sexual reproduction combines genetic material from two parents, producing offspring that are genetically distinct from either parent and from each other. In eukaryotes, this involves meiosis — a special form of cell division that produces gametes (sperm and egg in animals, pollen and ovules in flowering plants) with half the parent’s chromosome number. Fertilization — the fusion of two gametes — restores the full chromosome count and creates a new combination of alleles. Sexual reproduction is slower and more costly than asexual reproduction (finding a mate, producing gametes, risking half your genes on someone else’s offspring), but it generates the genetic variation on which natural selection acts.
Many organisms use both strategies. Aphids reproduce asexually during summer when conditions are favorable, then switch to sexual reproduction in autumn to produce genetically varied offspring that can survive winter. Fungi produce spores both sexually and asexually. The choice between strategies often reflects environmental conditions — stability favors cloning, uncertainty favors mixing.
Related terms
- Gene — the hereditary units transmitted through reproduction
- DNA — the molecule copied and recombined during reproduction
- Cell — the unit that divides in reproduction
- Natural selection — the evolutionary process that depends on the variation reproduction generates
- Species — defined in part by reproductive compatibility