MEIOSIS II : Meiosis II begins with prophase II --where spindle fibers form again and chromosomes condense once more. Metaphase II --this is where spindle fibers align chromosomes along the center of the cell. Anaphase II --this is where sister chromatids are separated and pulled to opposite poles of the cell. Telophase II --is where four haploid cells are produced by cytokinesis. Depending on the species and the sex of the organism, the cytokinesis that follows each meiotic division proceeds differently. In human males, all four haploid nuclei form sperm cells. In human females, only one of the four haploid nuclei forms and egg cell. The others do not survive. ** SEE FOLLOWING PAGE FOR DIAGRAM OF MEIOSIS.
Legend: Illustration of the process by which a single parent diploid cell (Both homologous chromosomes) divides to produce four daughter haploids cells (One homologous chromosome of the pair). Meiosis is the type of cell division by which germ cells (eggs and sperm) are produced. Meiosis involves a reduction in the amount of genetic material. Meiosis comprises two successive nuclear divisions with only one round of DNA replication. Four stages can be described for each nuclear division. First division of meiosis o Prophase 1: Each chromosome dupicates and remains closely associated. These are called sister chromatids. Crossing-over can occur during the latter part of this stage. o Metaphase 1 : Homologous chromosomes align at the equatorial plate. o Anaphase 1 : Homologous pairs separate with sister chromatids remaining together. o Telophase 1 : Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair. Second division of meiosis: Gamete formation o Prophase 2 : DNA does not replicate. o Metaphase 2 : Chromosomes align at the equatorial plate. o Anaphase 2 : Centromeres divide and sister chromatids migrate separately to each pole. o Telophase 2 : Cell division is complete. Four haploid daughter cells are obtained. One parent cell produces four daughter cells. Daughter cells have half the number of chromosomes found in the original parent cell and with crossing over, are genetically different. Meiosis differs from mitosis primarily because there are two cell divisions in meiosis, resulting in cells with a haploid number of chromosomes.
Unit 4: MEIOSIS New Chromosome Combinations Mitosis and meiosis are similar in that they are both forms of cell division, they include replication, there is the disappearance of the nucleus and nucleolus in both, and movement of chromosomes to opposite ends of the cell occurs in both. There are three main differences between mitosis and meiosis, however. 1. Meiosis produces daughter cells that have half the number of chromosomes found in the parent cell. Mitosis produces daughter cells with the same number of chromosomes as the parent cell.