Meiosis+Phases+Summary

The Phases of Meiosis Interphase: -the cell replicates its chromosomes -each chromosome has two sister chromatids held together by a centromere Prophase 1: -chromosomes coil up and a spindle forms -homologous chromosomes come together matched gene by gene forming a tetrad -Crossing Over may occur when chromatids exchange genetic material -this occurs two or three times per pair of homologous chromosomes -Crossing Over results in new combinations of alleles on a chromosomes Metaphase 1: -the centromere of each chromosome becomes attached to a spindle fiber -the spindle fibers pull the tetrads to the equator of the spindle -homologous chromosomes are lined up side by side as tetrads Anaphase 1: -homologous chromosomes separate and move to opposite ends of the cell -centromeres do not split -this ensures that each new cell will receive only one chromosome from each homologous pair Telophase 1: -the spindle breaks down and the chromosomes uncoil -the cytoplasm divides to yield two new cells -each cell has half the genetic information of the original cell because it has only one homologous chromosome from each pair Prophase II- -a spindle forms in each of the two new cells and the fibers attach to the chromosomes Metaphase II- -the chromosomes are pulled to the center of the cell and line up randomly at the equator Anaphase II- -the centromere of each chromosome splits -the sister chromatids separate and move to opposite poles Telophase II- -nuclei re-form -the spindles break down -the cytoplasm divides -identical to mitosis (Meiosis II) What Meiosis produces: -four haploid sex cells from one original diploid cell -each haploid cell contains one chromosome from each homologous pair -haploid cells will become gametes transmitting genes to offspring