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