Parthenogenesis occurs in the wild in many invertebrates (e.g. It has been documented in over 2,000 species. Parthenogenesis is a form of agamogenesis in which an unfertilized egg develops into a new individual. Examples are parthenogenesis and apomixis. Agamogenesis Īgamogenesis is any form of reproduction that does not involve a male gamete. Due to many environmental and epigenetic differences, clones originating from the same ancestor might actually be genetically and epigenetically different. In echinoderms, this method of reproduction is usually known as fissiparity. Each of these fragments develop into mature, fully grown individuals that are clones of the original organism. These fragments can take the form of soredia, dust-like particles consisting of fungal hyphae wrapped around photobiont cells.Ĭlonal Fragmentation in multicellular or colonial organisms is a form of asexual reproduction or cloning where an organism is split into fragments. Most lichens, which are a symbiotic union of a fungus and photosynthetic algae or cyanobacteria, reproduce through fragmentation to ensure that new individuals contain both symbionts. Some plants have specialized structures for reproduction via fragmentation, such as gemmae in mosses and liverworts. Many fungi and plants reproduce asexually. Animals that reproduce asexually include planarians, many annelid worms including polychaetes and some oligochaetes, turbellarians and sea stars. Each fragment develops into a mature, fully grown individual. Main article: Fragmentation (reproduction)įragmentation is a form of asexual reproduction where a new organism grows from a fragment of the parent. Fragmentation Linckia guildingi "comet", a starfish regrowing from a single arm However, mitotic sporogenesis is an exception and most spores, such as those of plants and many algae, are produced by meiosis. Thus the chromosome number of the spore cell is the same as that of the parent producing the spores. This method of reproduction is found for example in conidial fungi and the red algae Polysiphonia, and involves sporogenesis without meiosis. However, both events (spore formation and fertilization) are necessary to complete sexual reproduction in the plant life cycle.įungi and some algae can also utilize true asexual spore formation, which involves mitosis giving rise to reproductive cells called mitospores that develop into a new organism after dispersal. Since sexual reproduction is often more narrowly defined as the fusion of gametes ( fertilization), spore formation in plant sporophytes and algae might be considered a form of asexual reproduction (agamogenesis) despite being the result of meiosis and undergoing a reduction in ploidy. Meiosis and gamete formation therefore occur in separate multicellular generations or "phases" of the life cycle, referred to as alternation of generations. These haploid individuals produce gametes through mitosis. These spores grow into multicellular individuals called gametophytes, without a fertilization event. Plants and many algae on the other hand undergo sporic meiosis where meiosis leads to the formation of haploid spores rather than gametes. Exceptions are animals and some protists, which undergo meiosis immediately followed by fertilization. Many multicellular organisms produce spores during their biological life cycle in a process called sporogenesis. While all prokaryotes reproduce without the formation and fusion of gametes, mechanisms for lateral gene transfer such as conjugation, transformation and transduction can be likened to sexual reproduction in the sense of genetic recombination in meiosis. Komodo dragons and some monitor lizards can reproduce asexually. In vertebrates, the most common form of asexual reproduction is parthenogenesis, which is typically used as an alternative to sexual reproduction in times when reproductive opportunities are limited. Many eukaryotic organisms including plants, animals, and fungi can also reproduce asexually. Asexual reproduction is the primary form of reproduction for single-celled organisms such as archaea and bacteria. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the full set of genes of their single parent and thus the newly created individual is genetically and physically similar to the parent or an exact clone of the parent. Asexual reproduction in liverworts: a caducous phylloid germinatingĪsexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes.
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