Mitosis Meiosis Essay, Research Paper

Mitosis evolved in complex plants and animals for growth and repair. Mitosis, the

division of a cell resulting in two identical daughter cells, prolongs an organism s life by

replacing old, dead, and damaged cells. In complex animals and plants, mitosis occurs

everywhere, except sex cells.

Meiosis evolved in complex plants and animals to increase variation in offspring

and to maintain the number of chromosomes from generation to generation. Meiosis

occurs in the sex cells of organisms, specifically the ovaries and testes in animals, and in

the pollen and ovules of plants.

In an organism where n=8, the process of mitosis would be the following: In

interphase, the DNA would replicate, resulting in 16 chromosomes. In prophase, two

centrioles would move to the poles, the spindle starts to form, the nucleolus and nuclear

membrane disappear, and the kinetochore fibers attach to the chinetochores. During

metaphase, the chromosomes line up at the equator. In anaphase, the centromere splits,

and the chromosomes move to the opposite poles (8 to each pole), pulled by the

kinetochore fibers on the spindle. Lastly, during telophase, the spindle disappears, the

nucleolus and nuclear membrane reappear, and the cell separates resulting in two new

cells, exactly like the parent cell, each with 8 chromosomes.

Meiosis in an organism where n=8 would be the following: During interphase I,

the 16 chromosomes (2n=16) replicate to 32 chromosomes. In prophase I, centrioles

would move to the poles, the spindle starts to form, the nucleolus and nuclear membrane

disappear, and the kinetochore fibers attach to the chinetochores. Most importantly, the

pairing of homologous chromosomes and crossing over takes place. This step is very

important in creating variation among offspring. Next, the homologous pairs line up at

the equator in metaphase I. In anaphase I, the homologues, each consisting of two sister

chomatids separate, however the sister chromatids do not separate. During telophase I,

the spindle disappears, the nucleolus and nuclear membrane reappear, and the cell

separates resulting in two new cells, with different parts of each parent cell, each with 16

chromosomes. Within interphase II, cytokenesis occurs, and the cell is split in two.

Meiosis II closely resembles mitosis, except that the DNA does not replicate at

interphase. During prophase II, the nucleolus and nuclear membrane disappear, and

spindle fibers begin to appear. During metaphase, the chromosomes line up at the

equator. At anaphase II, the sister chromatids separate from each other. And in telophase

II, the spindle disappears, the nucleolus and nuclear membrane reappear, and the cells

separate resulting in four new cells, each with 8 chromosomes.

The major differences between mitosis and meiosis is that mitosis results in two

daughter cells exactly like the parent, whereas meiosis is sexual reproduction, resulting in

4 daughter cells that have a combination traits from both parents.