12/12/2007

meiosis

Meiosis produces germ cells, or gametes with half (haploid) the number of chromosomes of a diploid cell.

First cell division: single diploid parent cell successively passes through:
1. prophase 1
2. metaphase 1
3. anaphase 1
4. telophase 1 & prophase 2

Second cell division
5. metaphase 2
6. anaphase 2
7. telophase 2,
producing 4 haploid daughter cells.

(image mitosis vs meiosis)

Recombination provides a mechanism for genetic variability and is a mechanism of biological evolution. Recombination between homologous chromosomes in meiosis I involves the formation and repair of double strand breaks (DSBs), and meiosis I employs the same enzymes as does DSB repair. Many biologists consider the main function of sexual reproduction is to provide this mechanism for maintaining the integrity of the genome.

• A • adhesion • C • cell membranescellular adhesion moleculescellular signal transductioncentrioleschemotaxischloroplastcilia & flagellacommunicationconcentration gradientscytokine receptorscytoplasmcytoskeleton • E • energy transducersendoplasmic reticulumendosomesexosome • F • flagella & cilia • G • Golgi apparatusGPCRs • H • hormones • I • ion channels • L • lysosome • M • meiosismicrotubulesmitosismitochondrion • N • Nitric Oxideneurotransmissionneuronal interconnectionsnuclear membranenuclear pore • P • pinocytosisproteasomepumps • R • receptor proteinsreceptor-mediated endocytosis • S • second messengerssignaling gradientssignal transductionspindlestructure • T • transporttwo-component systems • V • vacuolevesicle

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