Meiosis The revision cards for all of your meiosis 4.0 / 5 based on 2 ratings ? BiologyCellular processes and structureA2/A-level Created by: Jake RichardsCreated on: 09-05-12 15:05 Prophase 1 Chromatin condenses and undergoes supercoiling chromsomes shorten and thicken they can absorb stains so can be seen The chromosomes come together in their homologous pairs They form a bivalent Each member of the pair has the same genes at the same loci Each pair has a paternal and maternal chromosome Non sister chromosomes wrap around each other The points they attach at are chiasmata Crossing over occurs and they swap sections of chromatids with each other Nucleolus disappears and nuclear envelope disintergrates Spindle forms and 1 of 9 Prophase 1 cont 2 of 9 Metaphase 1 Bivalents line up along the equator of the spindle the spindle is attached to spindle fibres along the centromere Chiasmata are still present Bivalents are arranged randomly each member of he homologous pair facing opposite poles Chromosomes indipendently segregate 3 of 9 Anaphase 1 The homologous chromosomes in each bivalent are pulled apart by the spindle fibres The centromeres do not divide The chiasmata separate and chromatid that have been crossed over remain with the chromatid where they have become newly attached 4 of 9 Telophase 1 Two nuclear envelopes form The cell divides by cytokinesis There is brief interphase Chromosomes uncoil 5 of 9 Prophase 2 If a nuclear envelope has formed, it is broken again The nucleolus disappears, chromosomes condense and spindles form 6 of 9 Metaphase 2 The chromosomes arrange themselves along the equator of the spindle The chromatids of each chromosome are randomly 7 of 9 Anaphase 2 The centromeres divide and chromatids are pulled apart. The chromatids randomly segregate 8 of 9 Telophase 2 Nuclear envelope reforms around the haploid daughter nuclei In animals, the two cells now divide to give four haploid cells In plants, a tetrad of four haploid cells is formed 9 of 9
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