The process of meiosis 0.0 / 5 ? BiologyCell replication - MeiosisASCCEA Created by: LucilleeCreated on: 24-04-17 14:35 Meiosis Occurs only in diploid cells Involves the separation of homologous chromsomes (meiosis 1) and the separation of chromatids (meiosis 2) 1 of 13 Prophase 1 Chromosomes condense; homologous chromosomes are paired and lie beside each other (known as a bivalent) Chromatids appear; they are entwined at points called chiasmata Chromatids may break at chiasmata and rejoin with a different chromatid (crossing over) 2 of 13 Metaphase 1 Bivalents move to the equator of the spindle Each chromosome attaches to the spindle via a centromere 3 of 13 Anaphase 1 Pulling by the spindle causes the chromosomes to move to opposite poles The chromsomes are separated, each still consisting of two chromatids 4 of 13 Telophase 1 Chromosomes reach opposite poles Nuclear membrane forms around each group of chromosomes (each nucleus has the haploid number of chromosomes) 5 of 13 Cytokinesis Cell divides to produce two daughter cells 6 of 13 Prophase 2 New spindle begins to form at right angles to the old spindle Cells are haploid Late prophase 2: nuclear membrane disintegrates 7 of 13 Metaphase 2 Chromosomes (consisting of chromatids) are arranged along the equator of the spindle 8 of 13 Anaphase 2 Sister chromatids are split at the centromere and pulled to opposite poles 9 of 13 Telophase 2 Each group of chromosomes become enclosed in a nuclear envelope In animal cells: constriction across the middle causes each cell to divide into two, creating four daughter cells (haploid), all genetically different In plant cells: four hapliod daughter cells, each possessing one member from the original pair of chromosomes is produced 10 of 13 The significance of meiosis Meiosis produces change Meiosis transforms the diploid condition into the haploid condition (vital for fertilisation) Meiosis produces genetically different cells (occurs as a result of crossing over and independent assortment) 11 of 13 Crossing Over Occurs as a result of chiasmata formation (late prophase 1) Results in each chromosome having a different combination of alleles (recombinants) 12 of 13 Independent Assortment During metaphase 1 bivalents are arranged at random along the equator The orientation of one homologous pair is not dependent on the orientation of any other When pulled apart during anaphase 1, chromosomes are likely to be separated 13 of 13
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