Meiosis

• Meiosis is also known as reduction devision.
• Mitosis is a special type of cell division of germ cells in sexually reproducing organisms used to produce the gametes such as sperm or egg cells. It involves two rounds of division that ultimately result in 4 cells with only one copy of each chromosomes.
• Gametes is also called sex cell.
• Mitosis only produces gametes: meiosis 1 and meiosis 2.
• Meiosis 1 - produces two haploid cells each containing one chromosome from the homologous pairs.
• Meiosis 2 - separates sister chromatids to produce four haploid gametes.
• Synapsis - pairing of homologous chromosomes.
• Tetrad - 4 sister chromatids of paired homologous chromosomes.
• Crossing over - recombination of alleles in homologous chromosomes.
• Result of crossing over - genetic variety in gametes.
• all gametes are haploid.
• Prophase 1 - starts with a diploid cell. Its chromatin contains two uncoiled spread out sets of chromosomes, one from each parent. After the DNA in the chromatin replicates, it condenses into the more familiar x shaped chromosomes.
• The replicated Dna is the same in the identical sister chromatid.
• The chromosomes contain genetic information called genes.
• These genes were inherited from each parent, and different versions of the same gene on each chromosomes are called alleles.
• Metaphase 1 - The homologous chromosomes line up the equator and attach to spindle fibers from opposite poles.
• Anaphase 1 - spindle fibers separate the homologous chromosomes in each tetrad and pull them to opposite poles of the cell.
• Telophase 1 - One chromosome from each homologous pair at separate poles. However, each chromosome still consists a sister chromatid. Each chromosomes sister chromatid is no longer identical because of the allele exchange that happened during crossing over. The spindle fibers disappear and the nuclear envelope membrane reforms around the chromosomes. Finally cytokinesis occurs.
• Prophase 2 - No DNA needed. The nuclear membrane disappears and spindle fibers fan out from the two sets of paired centrioles.
• Metaphase 2 - the chromosomes at each cell, line up in the equator and attach to the spindle fibers from both poles.
• Anaphase 2 - the sister chromotids of each chromosomes separate and move to opposite poles. Once the sister chromatid separate, they're called chromosomes.
• Telophase 2 - the spindle fibers dissapear and nuclear membranes reforms. And, cytokinesis occurs in both cells. Ends with 4 genetically different haploid daughter cells. Each containing only one set of chromosomes.