A life cycle is a period involving 1 generation of an organism through means of reproduction, whether through asexual reproduction or sexual reproduction. Generation (from the Greek γενεά) also known as procreation, is the act of producing Offspring. Reproduction is the Biological process by which new individual Organisms are produced Asexual reproduction is a form of reproduction which does not involve Meiosis, Ploidy reduction or Fertilization. The Evolution of sexual reproduction is a major puzzle The first Fossilized evidence of sexually reproducing Organisms is from Eukaryotes of the Stenian In regard to its ploidy, there are 3 types of cycles:
- haplontic life cycle
- diplontic life cycle
- diplobiontic life cycle (also referred to as diplohaplontic, haplodiplontic, or dibiontic life cycle)
These three types of cycles feature alternating haploid and all germinates. "Haplo" redirects here For the fictional character see The Death Gate Cycle. "Haplo" redirects here For the fictional character see The Death Gate Cycle. Germination is the process whereby growth emerges from a period of dormancy To return to a haploid stage, meiosis must occur (see Cell division). In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half Cell division is a process by which a cell, called the parent cell divides into two or more cells called daughter cells. The cycles differ in the product of meiosis, and whether mitosis (growth) occurs. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei Zygotic and gametic meioses have one mitotic stage and form: during the n phase in zygotic meiosis and during the 2n phase in gametic meiosis. Therefore, zygotic and gametic meiosis are collectively term haplobiontic (single mitosis per phase). Sporic meiosis, on the other hand, has two mitosis events (diplobiontic): one in each phase.
Contents |
Haplontic life cycle
A zygotic meiosis is a meiosis of a zygote immediately after karyogamy, which is the fusion of two cell nuclei. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half For other meanings see Zygote (disambiguation. A zygote (from Greek ζυγωτός zugōtos "joined" or "yoked" Karyogamy is the fusion of nuclei of two cells as part of Syngamy. In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed This way, the organism ends its diploid phase and produces several haploid cells. These cells divide mitotically to form either larger, multicellular individuals, or more haploid cells. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei Two opposite types of gametes (e. g. , male and female) from these individuals or cells fuse to become a zygote.
In the whole cycle, zygotes are the only diploid cell; mitosis occurs only in the haploid phase.
The individuals or cells as a result of mitosis are haplonts, hence this life cycle is also called haplontic life cycle. Haplonts are:
- Most fungi
- Some green algae
- Many protozoa
Diplontic life cycle
In gametic meiosis, instead of immediately dividing meiotically to produce haploid cells, the zygote divides mitotically to produce a multicellular diploid individual or a group of more unicellular diploid cells. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ The green algae (singular green alga) are the large group of Algae from which the Embryophytes (higher plants emerged Protozoa (in Greek πρῶτον proton "first" and ζῷα zoia "animals" are unicellular Eukaryotes (singular Cells from the diploid individuals then undergo meiosis to produce haploid cells or gametes. A gamete (from Ancient Greek γαμέτης; translated gamete = wife gametes = husband is a cell that fuses with another gamete Haploid cells may divide to form more haploid cells, as in many yeasts, but the haploid phase is not the predominant life cycle phase. In most diplonts, mitosis occurs only in the diploid phase, i. e. gametes usually form quickly and fuse to produce diploid zygotes.
In the whole cycle, gametes are usually the only haploid cells, and mitosis usually occurs only in the diploid phase.
The diploid multicellular individual is a diplont, hence a gametic meiosis is also called a diplontic life cycle. Diplonts are:
- Animals
- Some brown algae
- Some fungi, e. The Phaeophyceae or brown algae, (singular alga is a large group of mostly marine multicellular Algae including many Seaweeds of colder A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ g. brewer's yeast
Life history
The term "Life history" is better than "life cycle" especially for the red algae (Rhodophyta). The red algae (Rhodophyta ˌroʊdəˈfaɪtə roʊˈdɒfɨtə from Greek: ῥόδον (rhodon = rose + φυτόν (phyton = plant thus red plant are In the Rhodophyceae there are generally three stages and thus "alternation of generations" is not suitable. [1]
Life history theory
In animal and human biology life history theory is a method of understanding evolved behaviors and strategies to optimize reproductive success. Life history theory is an analytical framework widely used in animal and human Biology, Psychology, and Evolutionary Anthropology which postulates
References
- ^ Dixon, P. S. 1973. Biology of the Rhodophyta. Oliver & oyd, Edinburgh. ISBN 0 05 002485 X
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic