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Lecture 22

BIOL 1020 Lecture 22: Lecture 22

3 Pages

Biological Sciences
Course Code
BIOL 1020
Joy Stacey

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Lecture 22 Meiosis Split into meiosis 1 and meiosis 2 meiosis 1 goes from 2n double stranded to 1n double stranded meiosis 2 goes from 1n double stranded to 1n single stranded o Division in meiosis I occurs in four phases: Prophase I Metaphase I Anaphase I Telophase I and cytokinesis Cell goes through all of these phases as a continuum Prophase I Typically occupies more than 90 of the time required for meiosis Chromosomes begin to condense In synapsis, homologous chromosomes loosely pair up, aligned gene by gene. In crossing over, non sister chromatids exchange DNA segments Each pair of chromosomes forms a tetrad, a group of four chromatids o Tetrad consists of a homologous pair referred to as tetrad during prophase I Each tetrad usually has one or more chiasmata, X shaped regions where crossing over occurs. Metaphase I In metaphase I, tetrads line up at metaphase plate, with the one chromosome facing each pole Microtubules from one pole are attached to the kinetochore of one chromosome of each tetrad Microtubules from the other pole are attached to the kinetochore of the other chromosome Anaphase I Pairs of homologous chromosomes separate One chromosomes moves toward each pole, guided by the spindle apparatus Sister chromatids remain attached at the centromere and move as one unit toward the pole Telophase I cytokinesis In the beginning of telophase I, each half of the cell has a haploid set of chromosomes each chromosome still consists of two sister chromatids
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