ABSTRACT
https://www.niso.org/standards/z39-96/ns/oasis-exchange/table"> Cell cycle The cell cycle describes all the events that occur in a cell from the end of one cell division to the end of the next. There are four phases in the eukaryotic cell cycle, which include cell growth (G1), DNA synthesis (S), a second gap or growth phase (G2), and finally nuclear division (M phase). Vlitosis and asexual cell division Mitosis is nuclear division that results in progeny nuclei that are identical to the parent. It is usually followed by cytokinesis, cell division, which produces cells that have the same phenotype as the parent. In some eukaryotic microbes multiple nuclear divisions may occur without cytokinesis, giving rise to large, multinucleate cells. There are four stages of mitosis, prophase, metaphase, anaphase, and telophase. During prophase chromosomes duplicate to form chromatids, joined at the centromeres. Centromeres are attached to spindle microtubules. During metaphase, chromatids are arranged across the center of the cell, and during anaphase the microtubules pull the sister chromatids apart to the poles of the dividing cell. During telophase the microtubules disappear and the nuclear envelopes fuse. Vleiosis and sexual cell division Meiosis is a nuclear division where there is a halving of chromosome numbers from a diploid to a haploid state. In organisms with an extended diploid phase of their life cycle, meiosis produces haploid gametes, and it is immediately followed by gamete fusion and formation of a new diploid organism. In organisms with an extended haploid stage, diploid formation is immediately followed by meiosis which produces the new haploid organism. There are eight stages to meiosis; prophase 1, metaphase 1, anaphase 1, and telophase 1, and prophase 2, metaphase 2, anaphase 2, and telophase 2. During prophase 1, homologous chromosomes associate and duplicate. At this point there may be recombination. During metaphase 1, homologous chromosomes assemble on the spindle across the cell, and they are separated during anaphase 1 and telophase 1. Prophase and metaphase 2 are transient and the chromatids assemble across the cell to be separated during anaphase 2. During telophase 2 cell division usually occurs. Chromosomes Eukaryotic microorganisms package the large amount of DNA they contain into chromosomes. Chromosomes contain a single, linear double strand of DNA tightly bound with histone proteins. There are usually between four and eight chromosomes per cell. Histones Histones are basic proteins that bind to DNA to condense and fold it. They are vital to the structure of DNA and have been highly conserved during evolution. Related topics
Cell division
Genomes
DNA replication
Recombination
Reproduction in fungi
Archaeplastida, Excavata, Chromalveolata, and Amoebozoa: life cycles
191