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Name __________________________________________________________________ Meiosis Reading The products and purposes of mitosis and meiosis are drastically different. The purpose of mitosis is to create new body cells (somatic cells) and the purpose of meiosis is to produce reproductive cells (gametes), sperm in men and eggs in women. Mitosis produces two, genetically identical, diploid offspring. Meiosis produces four, genetically unique, haploid offspring. Mitosis is an example of asexual reproduction and Meiosis is sexual reproduction. We know the cell cycle is made up of the following phases: Interphase (G1, S, G2), Mitosis (Prophase, Metaphase, Anaphase, Telophase), and Cytokinesis. Meiosis is essentially the same, but it goes through two round of division called “Meiosis I” (Prophase I, Metaphase I, Anaphase I, Telophase I, and Cytokinesis I) and “Meiosis II” ((Prophase II, Metaphase II, Anaphase II, Telophase II, and Cytokinesis II). Two rounds of division ensure that each daughter cell is haploid. Genetic variation is caused in two main ways in Meiosis. First, “crossing over” creates unique combinations of genes on the chromosomes. Second, the two rounds of cellular division and splitting of chromosomes creates unique combinations of chromosomes in the daughter cells. 1. Crossing Over: genes are exchanged between a pair of homologous chromosomes. During meiosis, homologous pairs of chromosomes line up next to each other (example: Chromosome 1 from biological mother lines up with Chromosome 1 from biological father). They are so close together that they exchange genes. The resulting chromosomes now have completely new combinations of genes. For example, the gene for eye color (blue) from your biological mother on chromosome 1, just got switched with the gene for eye color (brown) from your biological father on chromosomes 1. 2. Chromosome Shuffling: depending on how homologous pairs line up in the center of the cell before splitting, the daughter cells will have different combinations of chromosomes than the original cell and from each other. One cell may get more original chromosomes from the biological father and another cell may get more original chromosomes from the biological mother. Why is genetic variation important? Genetic diversity plays an important role in the survival and adaptability of a species. When a population's habitat changes (climate, food availability, new pathogens that cause disease, new competition for food, etc.), the population will have to adapt to survive. Variation in the population's gene pool provides new traits among the individuals of that population. These variable traits can be selected for, via natural selection, ultimately leading to an adaptive change in the population, allowing it to survive in the changed environment. If a population of a species has a very diverse gene pool then there will be more variety in the traits of individuals of that population and consequently more traits for natural selection to act upon to select the fittest individuals to survive. Genetic diversity is essential for a species to evolve. With very little gene variation within the species, healthy reproduction becomes increasingly difficult, and offspring are more likely to have problems resulting from inbreeding. The vulnerability of a population to certain types of diseases can also increase with reduction in genetic diversity. If organisms reproduced asexually, new genes would occur much less frequently in the population, which means that organisms would adapt too slowly to changing conditions and species would die out.