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lecture_2.page03 - Meiosis Meiosis I(= reductional division...

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Unformatted text preview: Meiosis Meiosis I (= reductional division) Stages: Leptotene: chromosomes attach themselves by telomeres to the inner membrane of nuclear envelope. Lateral (axial) elements (of synaptonemal complex) are formed. Zygotene: homologues pair at their telomeres and begin to synapse forming the synaptonemal complexes. Pachytene: pairing (synapsis) is completed and crossing over is executed. Diplotene: homologous chromosomes are beginning to repulse each other, chiasmata form. Diakinesis: bivalents move to the equator of the cell. Metaphase I: bivalents orient themselves on the equator. Chiasmata are on the equator and homologous centromeres point at the opposite poles. Anaphase I: homologous chromosomes move to the opposite poles. Telophase I: a diad of daughter nuclei is formed. The nuclei have reduced chromosome number (they are haploid). Interkinesis: resting stage between meiosis I and II. N 0 DNA replication occurs! Meiosis II (= equational division) Prophase II: chromosomes condense. Metaphase II: chromosomes orient themselves on the equator with their centromeres. Anaphase II: Sister chromatids move to the opposite poles. Telophase II: Four haploid nuclei are formed. Ultimately, four cells (tetrad) develop. ...
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