Youtor
Mitosis The Amazing Cell Process that Uses Division to Multiply Updated
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For more information, log on to- • http://shomusbiology.weebly.com/ • Download the study materials here- • http://shomusbiology.weebly.com/bio-m... • Meiosis Listeni/maɪˈoʊsɨs/ is a special type of cell division necessary for sexual reproduction in eukaryotes. The cells produced by meiosis are gametes or spores. In many organisms, including all animals and land plants (but not some other groups such as fungi), gametes are called sperm and egg cells. • Whilst the process of meiosis bears a number of similarities with the 'life-cycle' cell division process of mitosis, it differs in two important respects: • eiosis begins with one diploid cell containing two copies of each chromosome—one from the organism's mother and one from its father. The cell divides twice, potentially producing up to four haploid cells containing one copy of each chromosome. ( Potentially because in some cases, such as the formation of oocytes in mammals, only one of the possible four haploid cells survives.) In animals the haploid cell resulting from meiosis is a male or female gamete. Each of the resulting chromosomes in the gamete cells is a unique mixture of maternal and paternal DNA, resulting in offspring that are genetically distinct from either parent. This gives rise to genetic diversity in sexually reproducing populations. This genetic diversity can provide the variation of physical and behavioural attributes (phenotypes) upon which natural selection can act. • It is also noteworthy that during meiosis, specific genes are more highly transcribed, and these are called the meiome, the term used in functional genomics for the meiotic transcriptome.[1][2] Meiosis is a key feature for all sexually reproducing eukaryotes in which homologous chromosome pairing, synapse and recombination occur. In addition to strong meiotic stage-specific expression of mRNA (the meiome), however, there are also pervasive translational controls (e.g. selective usage of preformed mRNA), regulating the ultimate meiotic stage-specific protein expression of genes during meiosis.[3] Thus, both the meiome and translational controls determine the broad restructuring of meiotic cells needed to carry out meiosis. • Prior to the meiosis process the cell's chromosomes are duplicated by a round of DNA replication, creating from the maternal and paternal versions of each chromosome (homologs) two exact copies, sister chromatids, attached at the centromere region. In the beginning of meiosis, the maternal and paternal homologs pair with each other. Then they typically exchange parts by homologous recombination leading to crossovers of DNA between the maternal and paternal versions of the chromosome. Spindle fibers bind to the centromeres of each pair of homologs and arrange the pairs at the spindle equator. Then the fibers pull the recombined homologs to opposite poles of the cell. As the chromosomes move away from the center the cell divides into two daughter cells, each containing a haploid number of chromosomes composed of two chromatids. Source of the article published in description is Wikipedia. I am sharing their material. Copyright by original content developers of Wikipedia. • Link- http://en.wikipedia.org/wiki/Main_Page PPT source: All the PowerPoint material is from Sciencegeek.net. Copyright by sciencegeek.net. • Link- http://www.sciencegeek.net/Biology/Po...
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