Asexual Reproduction or Apomixis

Abstract

Reproduction is asexual (apomictic) when it occurs without recombination. Apomixis (Greek apo = without, mixis = mingling) is the general term for it. The simplest case is found in unicellular plants and animals where there is doubling of cytoplasmic contents and replication of genetic material followed by division of the cell into two parts. Most reproduction in bacteria, blue-green algae, unicellular algae, and protozoa takes place in this way. These organisms may form resistant cells with dense cytoplasm replete with food reserves and with heavy protective cell wall. These cells permit the species to endure unfavorable conditions and frequently effect dispersal. Multicellular plants may also reproduce by single cells that have been formed by mitotic divisions (mitospores). Sometimes they are flagellated and actively disperse. Sometimes they are resistant structures. Flagellated mitospores occur only in plants that inhabit rivers, ponds, lakes, ocean, watery surface-films, or the watery medium of a host in which they live. Many algae and algal-like fungi (Phycomycetes) have flagellated mitospores. Those fungi completely adapted to terrestrial existence—higher Phycomycetes and Ascomycetes—produce nonflagellated mitospores that are passively dispersed in air. These spores are frequently cleaved off at the tips of hyphae and are called by specialized names depending on the group in question. In Ascomycetes and Fungi Imperfecti these are the conidiospores.