Metaphase i spindle fibres from opposing centrosomes

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Metaphase I Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) Homologous pairs of chromosomes align along the equator of the cell.
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Anaphase I Spindle fibres contract and split the bivalent Homologs separate and move to opposite poles. Sister chromatids remain attached at their centromeres .
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Telophase I Chromosomes decondense. Nuclear envelopes may reassemble. Spindle disappears. Cytokinesis divides cell into two haploid daughter cells.
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Prophase II: No interphase No crossing over Spindle forms Metaphase II: Chromosomes line up Anaphase II: Sister chromatids separate Telophase II: 4 haploid cells Nuclei reappear Each daughter cell genetically unique Meiosis II (2nd division) = create gametes - 4 phases
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Meiosis II Only one homolog of each chromosome is present in the cell . Meiosis II produces gametes with one copy of each chromosome and thus one copy of each Sister chromatids carry identical genetic information . Gene X
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Meiosis II: Reducing Chromosome Number Prophase II Metaphas e II Anaphas e II Telophas e II 4 Identical haploid cells
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Prophase II Chromosomes condense, nuclear membrane dissolves, centrioles move to opposite poles (perpendicular to before) Nuclear envelope fragments.
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Metaphase II Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) Chromosomes align along equator of cell .
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Anaphase II Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles Sister chromatids separate and move to opposite poles . Equator Pole
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Telophase II Nuclear envelope reassembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two to form four haploid daughter cells .
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Results of Meiosis Gametes (egg & sperm) form Four haploid cells with one copy of each chromosome One allele of each gene Different combinations of alleles for different genes along the chromosome
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3 Sources of Genetic Variation: 1. Crossing Over Exchange genetic material Recombinant chromosomes Offspring with recombinant chromosomes will have unique gene combinations that are not present in either parent
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1. Independent Assortment of Chromosomes Random orientation of homologous pairs in Metaphase I When they line up, their orientation towards the opposing poles is random , as is the subsequent assortment of chromosomes into gametes The orientation of each bivalent occurs independently , meaning different combinations of maternal / paternal chromosomes can be inherited when bivalents separate in Anaphase I The final gametes will differ depending on whether they got the maternal or paternal copy of a chromosome after Anaphase I.
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