Northwest Vista College, Biology 1406 LaboratoryMeasurementsMeiosisMeiosis begins with a diploid cell (2n=46 in humans) and produces haploid (n=23 in humans) cells called gametes. Gametes are sex cells and specifically include egg and sperm. In diploid cells, there are two chromosomes of each type which are called homologous chromosomes. Each of the homologous chromosomesarises from the parents. In animals, meiosis produces gametes that have only one chromosome of each pair of homologous chromosomes.Just as in mitosis, chromosomes are duplicated during Interphase I of meiosis forming sister chromatidsheld together at the centromere. Also, microtubules of a spindle apparatus move chromosomes. However, meiosis has two consecutive divisions called Meiosis I and Meiosis II. Between Meiosis I and II (in Interphase II), DNA is not duplicated. Therefore, at the end of meiosis there are four haploid nuclei.During Prophase I, important events that contribute to genetic diversity take place. Both maternal and paternal replicated homologous chromosomes align closely together forming a four-stranded structure called a tetrad. The alignment process is called synapsis (“syn” means together). Synapsis gives rise to an event called crossing over, in which genes between nonsister chromatids are exchange reciprocally. Also during Prophase I, the nuclear envelope is disassembled and microtubules are able to attach to the tetrads. During Metaphase I tetrads align at the midline of the cell. In Anaphase I the tetrads split and sister chromatids move towards opposite sides of the cell with the aid of microtubules. Telophase I and cytokinesis create two haploid cells which still contain replicated DNA.Meiosis II is essentially the same as mitosis in regards to the mechanics of the events that occur. However, the end result is very different. In Prophase II, microtubules attach to the sister chromatids. Sister chromatids align at the middle of the two cells in Metaphase II. During Anaphase II, sister chromatids finally split and the daughter chromosomes move to opposite sides in both cells. Telophase II and cytokinesis creates four haploid cells that are genetically different from each other and the original cell.Plants do undergo meiosis! However, the resulting cells are called spores, not gametes. (See previous section of this lab for further information.)Exercise 1: Self-guided Activity with Popbeads (meiosis)Guidelines for the Meiosis Popbead Exercise1.Make two yellow pop bead chromosomes 20 beads long with a magnet between the 10thand 11thbeads for each. Make two red pop bead chromosomes 20 beads long with a magnet between the 10thand 11thbeads foreach. Grab 4 plastic bags. Now, place one yellow chromosome and one red chromosome in a place where you do NOT see them, but they are still accessible.