Alternation (alternation of generations) Generational phenomenon refers to the biological life cycle, resulting in spore form for generations (asexual generation) and gamete gametophyte generation (sexual generation) regularly alternating. Generational plants Generational plants with ferns obvious, sporophyte and gametophyte can live independently. When the body is diploid asexual spores, pollen mother cells through meiosis to produce haploid (n) of the spores germinate grow into small, independent living gametophyte, called prothallus. When prothallium during sexual reproduction, differentiated male and female sexual organs, namely archegonium sperm device and produce eggs and sperm, respectively. Both gametes with the formation of a diploid (2n) zygote. Zygote grow into the next generation of new sporozoites. Generational change in all types of plants, because the spores gametophytes and morphology, size, significantly different sex, life duration and whether other aspects of independent living, very different, but the basic process is the same and ferns. Flora generational change can be divided into two types (based on complexity, significant life cycle of life and independence of sporophyte and gametophyte morphology, size, structure): ① etc. or the same type of generational generational. In the history of life sporophyte and gametophyte outer shape, size, structure and significantly exactly the same, no difference, and be able to live independently, but there is a diploid number of chromosomes in cells of two individuals (2n) and haploid ( n) the difference, called generational change or the same type of generational change, etc., this type we saw in algae. ② ranging from generational or shaped generational. In the history of life sporophyte and gametophyte look poor. According to the form of two generations, the size and the availability of independent living functions, can be divided into: type of generational moss, fern type of generational and seed plant-generational. Animal generational Animals found in a variety of generational invertebrates, differ in protozoa and metazoans. Some alternate process performance for different individuals generation change generation; but also some kind of individual self was only replaced by another kind of stretches after several generations, a phenomenon known as alternating different states. Alternating asexual generations in a generation for the individual and the other individual on behalf of a sexual, generational change, he said asexual and sexual; unisexual generation to another generation, took the opposite gender for generations called alternation. ◆ protozoa generational In fact, sexual reproduction alternate generations and generations of asexual reproduction, is generational lower form. In protozoa in alternation, alternating sexual and asexual individuals do not necessarily have the appropriate individual relationships with alternating haploid and diploid generations generations; and sexual generation or asexual generations may belong to haploid generation or with diploid generations. Generational protozoa can be divided into the following three types: ① haploid phase with generational. Sexual generation and asexual generation individuals are haploid, with only the non-born diploid cells, such as Chlamydomonas and some spores insects animals. ② diploid with phase alternation of generations. In addition to haploid gametes period, all asexual and sexual generation are of diploid individuals, such as worms and ciliates some sun animals. ③ phase generational differences. Asexual diploid, haploid sexual generations, and fern spores body diploid haploid gametophyte consistent, as part of foraminifera animals. ◆ multicellular invertebrates generational Multicellular invertebrates generational following three types: ① alternating asexual and sexual generations. As polyp cnidarians alternate generations and generations of medusa. Sessile polyp is asexual life, freedom camp life medusa is the sexual generation. ② ease of generational change. Some single nest as single-sex class of rotifer generations is dormant eggs (or egg winter) develop into a female. Such individuals do not need to fertilize spring and summer only produce that is capable of developing a non-sperm and thus need to repeat several generations. After the season under the influence of environmental change, non-need sperm can produce two kinds of females. A thick shell females need sperm output, form resting eggs after fertilization, the shell of another female body needs to produce sperm and develop into males without fertilization. So this male body and the production of sperm thick shell of females need common form of gender generations. ③ haploid and diploid generations alternate generations. This is based on chromosome number is converted to life ring, generational implications in relaxing under the proposed concept, haploid gametophyte generation, sporophyte is a diploid generations. Animal and higher plants are diploid generation is dominated by fungi are haploid dominant. From an evolutionary point of view, than the diploid haploid more advantages. The reason is the diploid formed by profiled joining can collect or store the one hand, many a time does not work and will be lost in the haploid genes, so that the potential variability of gene combinations can be improved, through genetic mechanisms conducive to production the more adaptable species freshmen; on the other hand due to the recessive gene expression fewer opportunities to spread slowly alleviate the effects of natural _select_ion pressures, so the organism can be too late to avoid a sudden choose to make rapid response. Conversely, if no such action recessive gene mutation organism will become more intense. Tau Chi illustration insect (obelia, one for Tau Chi intestinal worm) medusa generations and generations of polyps alternately.
Asexual diploid, haploid sexual generations, and fern sporophyte diploid haploid gametophyte consistent, as part of foraminifera animals. Tau Chi illustration insect (Obelia, one for Tau Chi intestinal worm) medusa generations and generations of polyps alternately.
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English Expression
: alloiobiogenesis, alloiogenesis
n.: digenesis, heterogamy, heterogenesis, heterogony, metagenesis, xenogenesis, alternation of generations