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It is the stage of the life cycle when a cell gives rise to haploid cells each having half as many chromosomes as the parental cell. Two such haploid gametes, ordinarily arising from different individual organisms , fuse by the process of fertilization , thus completing the sexual cycle.
In eukaryotic cells, asexual division occurs by mitosis and cytokinesis, while specific lineages of cells reserved for sexual reproduction can additionally divide by meiosis. [6] cell fusion The merging or coalescence of two or more cells into a single cell, as occurs in the fusion of gametes to form a zygote.
The origin of the eukaryotic cell, or eukaryogenesis, is a milestone in the evolution of life, since eukaryotes include all complex cells and almost all multicellular organisms. The last eukaryotic common ancestor (LECA) is the hypothetical origin of all living eukaryotes, [71] and was most likely a biological population, not a single ...
Prokaryotic cells are distinguished from eukaryotic cells by the absence of a cell nucleus or other membrane-bound organelle. [10] Prokaryotic cells are much smaller than eukaryotic cells, making them the smallest form of life. [11] Prokaryotic cells include Bacteria and Archaea, and lack an enclosed cell nucleus. Eukaryotic cells are found in ...
The eukaryotic cell cycle consists of four distinct phases: G 1 phase, S phase (synthesis), G 2 phase (collectively known as interphase) and M phase (mitosis and cytokinesis). M phase is itself composed of two tightly coupled processes: mitosis, in which the cell's nucleus divides, and cytokinesis, in which the cell's cytoplasm and cell membrane divides forming two daughter cells.
Under the strict definition of isogamy, fertilization occurs when two gametes fuse to form a zygote. [8] Sexual reproduction between two cells that does not involve gametes (e.g. conjugation between two mycelia in basidiomycete fungi), is often called isogamy, although it is not technically isogametic reproduction in the strict sense. [1]
Sexually reproducing animals, plants, fungi and protists are thought to have evolved from a common ancestor that was a single-celled eukaryotic species. [1] [2] [3] Sexual reproduction is widespread in eukaryotes, though a few eukaryotic species have secondarily lost the ability to reproduce sexually, such as Bdelloidea, and some plants and animals routinely reproduce asexually (by apomixis ...
Eukaryogenesis, the process which created the eukaryotic cell and lineage, is a milestone in the evolution of life, since eukaryotes include all complex cells and almost all multicellular organisms. The process is widely agreed to have involved symbiogenesis , in which an archaeon and a bacterium came together to create the first eukaryotic ...