Meiosis Flashcards for the phases of Meiosis 1 and 2 3.0 / 5 based on 1 rating ? BiologyCellular processes and structureA2/A-level Created by: Katie WardCreated on: 19-04-12 17:25 Meiosis Sexual reproduction Causes genetic variation The gametes of each parent fuse to form a zygote When the gametes fuse, the chromosomes combine in one nucleus. This means that the chromosome number is diploid. The role of meiosis is to reduce the chromosome number by half, therefore making it haploid. These phases are preceeded by Interphase 1, where DNA and organelles replicate. 1 of 9 Prophase 1 Chromatin undergo supercoiling Homologous pairs of chromosome form bivalents Non-sister chromatids wrap around each other - chiasmata Non-sister chromatids swap DNA - crossing over Nucleolus disappears Nuclear envelope disintegrates Spindle forms Can last for several days 2 of 9 Metaphase 1 Bivalents join up across the equator They are joined to spindle at centromeres The chromosomes are ready to independently segregate 3 of 9 Anaphase 1 Homologous chromosomes are pulled by the spindle to opposite poles The centromeres don't divide Chiasmata separate - the swapped lengths of DNA stay with their new chromosome 4 of 9 Telophase 1 Two new nuclear envelopes form Brief interphase In plants, the cell goes straight from anaphase 1 into meiosis 2 5 of 9 Prophase 2 Nuclear envelope breaks down again Nucleolus disappears Chromosomes supercoil Spindle form 6 of 9 Metaphase 2 Chromosomes arrange themselves on the spindle, 90 degrees to how they were arranges in metaphase 1 Chromatids are randomly assorted 7 of 9 Anaphase 2 Centromeres divide Chromatids are pulled to opposite poles 8 of 9 Telophase 2 Nuclear envelopes reform around haploid daughter nuclei In animals, 4 haploid cells form In plants, a tetrad of four haploid cells is formed 9 of 9
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