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, ce
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.