Meiosis vs. Mitosis essays

Meiosis vs. Mitosis essays Major Comparisons Between Meiosis and Mitosis The two processes of nuclear division are similar as in they allow cells to divide and reproduce, but they also have many differences. Meiosis is the type of nuclear division that occurs in sexually reproducing organisms. In meiosis, the diploid number of chromosomes is reduced to the haploid number. Gametes have the haploid number, while zygotes have the diploid number. The homologous chromosomes that appear in the zygote look alike and have the same length and centromere position, but the genes they hold may be for opposing traits. After duplication, the homologues become sister chromatids that are joined together at the centromere. Meiosis also has two cell divisions, meiosis I and meiosis II. Synapsis occurs at the start of meiosis I. The lining up of the homologues results in a bivalent, two homologous chromosomes that stay together during the initial phases of meiosis I. After synapsis, the homologous chromosomes separate and the daughter cells have one copy of each kind of chromosome. During meiosis II, the daughter chromosomes move to opposite poles, leaving the chromosomes with only one chromatid each. The main purpose of meiosis is to keep the chromosome number constant generation after generation. If not for meiosis, the chromosome number would continue to increase inevitably. It also ensures that genetic recombination will occur. Genetic recombination makes it so that offspring do not have the same combination of genes as their parents. One way this is achieved is through crossing-over. Crossing-over is the process of distribution of the homologues to different daughter cells during synapsis. The genetic instructions from a mother and father are mixed and the joined chromatids are no longer identical. The other key way for genetic recombination to occur is through independent assortment. When homologues align at the metaphase plate, the mate ...