AP Biology Meiosis Essay

Meiosis is the process in sexually reproducing organisms where cells divide. The cells produced during meiosis have half the chromosome number as the original cell. There are two cell divisions in meiosis, meiosis l and meiosis ll. These cell divisions produce 4 hapolid daughter cells. Haploid cells contain only one set of chromosomes, which is written as n. Meiosis consists of nine phases. In meiosis the interphase l the chromosomes replicate and the centrosome duplicates in one diploid cell. Diploid cells have two sets of chromosomes, they received one from each parent. During prophase l the nuclear envelope fragments and spindle microtubules form between the centrosomes. Homologous chromosomes pair to make two sister chromatids. This is called synapsis. Chromatids of homologous pairs exchange segments when they cross over. At metaphase l, the pairs line up on the metaphase plate.

Microtubules from one pole attach to the kinetochore of one homologous chromosome, while microtubules from the other pole attach to the kinetochore of the other pair. During anaphase l the microtubules get shorter pulling the homologous pairs towards opposite poles. At telophase l two haploid cells form but the chromosomes are still double. Meiosis ll separates the sister chromatids. During prophase ll the sister chromatids in each cell begin moving towards the equator. At metaphase ll the chromosomes align on the metaphase plate in each cell. The process of anaphase ll pulls the sister chromosomes to opposite poles in each cell. During telophase ll each cell forms a nuclei and cytokinesis splits the cells apart. Four genetically different haploid cells are produced.

Independent assortment is differences between the genes. Variation can occur in meiosis when the chromosomes cross over and during random fertilization. Random fertilization is when a gamete from the mother unites with the haploid from the father to produce a diploid zygote. The gamete from the mother is one of 8 million and the gamete from the father is one of 8 million. Independent assortment occurs during prophase ll of meiosis l. The Law of Segregation is Mendel’s first law, which states that allele pairs separate during gamete formation, and then randomly re-form as pairs during the fusion of gametes at fertilization.