Meiosis and Mitosis
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Mitosis and meiosis are the means by which reproduction takes place. Mitosis creates an exact duplicate of cell so that old cells can be replaced, such as in skin, hair, and bones. Meiosis allows a cell to unite one half of its genetic makeup with a cell from another partner to create an entirely new organism.
Mitosis
Mitosis is the process by which two daughter cells are formed, each containing a complete set of chromosomes. Mitosis is the process by which an organism creates new cells, such as skin or bone. There are two parts to a cells life – interphase and mitosis. Interphase is the normal life of the cell when all of the growth and metabolism processes take place. Mitosis happens after interphase is complete and produces an exact replica of the parent cell. There are four steps in mitosis where the cell itself goes through different stages of change. These steps are called prophase, metaphase, anaphase, and telophase.
During Prophase the chromatin coils to form visible chromosomes. In early prophase, the DNA and centrioles duplicate. In middle prophase the centrioles make microtubules that attach to the DNA. In late prophase, the spindle is formed. The chromosomes start to move toward the center of the cell.
The chromosomes line up on the equator of the spindle in metaphase. The spindle, made of microtubules connecting the chromosomes to the centrioles, begins to pull on the DNA strands.
Anaphase is the next step. Now, in anaphase the DNA strands split and the sister chromatids, one half of each DNA strand, are pulled apart to the centrioles at the opposite ends of the cell.
Telophase is the final phase or mitosis. During telophase, the plasma membrane pinches the cell and forms two completely separate cells that are exact duplicates of the parent cell.
There are now two new daughter cells, each with its own nucleus.
Meiosis
Meiosis is a type of cell division where one body cell produces four gametes, each containing half the number of chromosomes as a parents body cell. Meiosis allows for sexual reproduction where DNA from two parents combines to from an offspring. Meiosis is broken into two parts called Meiosis I and Meiosis II.
Meiosis I
The stages of Meiosis I are called prophase I, metaphase I, anaphase I, and telophase I. Prophase I is like prophase in mitosis. However, in metaphase I, instead of pulling the chromosomes away from their duplicates, the microtubules attach so as to pull the like pairs, called homologues, apart and leave the chromosomes attached to their duplicates.
In anaphase I, the microtubules of the spindles pull the homologues apart.
In telephase I, the plasma membrane pinches the cell into two parts and the chromosomes are surrounded by nuclear material. At the end of meiosis I, two haploid