Mitosis and Meiosis describes the process by which the body prepares cells to participate in either asexual or sexual reproduction to make an entire organism.
Examples of Mitosis and Meiosis
Mitosis is the
reproduction of skin, heart, stomach, cheek, hair etc. cells. These
cells are "Autosomal" cells. This is also a form of "Asexual"
reproduction, where one organism or cell reproduces itself. Some
organisms that reproduce asexually are hydra, bacteria, and single
celled organisms.
"A" greek meaning "without."
"Sex" Greek meaning "to cross."
Meiosis is the
production of sperm and egg cells. These cells are "Gamete" or "Sex"
cells. Each cell has to go through the division process twice in order
for the cell to end up with half the number of chromosomes. The cells
pass on genetic information to the offspring. This is a form of
"Sexual" reproduction, where one organism or cells reproduces by
crossing with another organism or cell. Types of organisms that
reproduce sexually are; plants, animals, and insects.
For either of these processes of reproduction we must
first understand the basic Chromosome structure that the body uses in
either Mitosis or Meiosis.
Mitosis: --One cell becomes two cells-- The new
"daughter" cell has exactly the same number of chromosomes and
information as the "parent" cell. 1 cell divides and becomes 2 cells.
Meiosis: --One cell becomes 4 cells--There are 4 new "daughter" cells. Each new gamete cell contains only one-half
of the number of chromosomes of the parent cell. Each sex cell goes
through the division process twice in order to have the correct number
of cells, and the correct chromosomal information. (Look carefully at
the diagram below to understand how each chromatid becomes part of a
new sperm or egg cell. Go back to the first diagram if necessary to
study what a chromosome pair, chromatid, and allele is.)
In
female mammals (humans too) 3 of the gametes do not mature with a full
yoke sack. Only 1 of the 4 can become a mature egg. All mature eggs are
formed to a certain stage in the first division.
In male mammals (humans too) all 4 gametes mature into sperm cells. The
male is continually forming these after birth.
Meiosis and Mitosis describe cell division in eukaryotic cells when the chromosome separates.
In
mitosis chromosomes separates and form into two identical sets of
daughter nuclei, and it is followed by cytokinesis (division of
cytoplasm). Basically, in mitosis the mother cell divides into two
daughter cells which are genetically identical to each other and to the
parent cell.
Phases of mitosis include:
1. Interface -where cell prepares for cell division and it also
includes three other phases such as G1 (growth), S (synthesis), and G2
(second gap)
2. Prophase – formation of centrosomes, condensation of chromatin
3. Prometaphase- degradation of the nuclear membrane, attachment of microtubules to kinetochores
4. Metaphase- alignment of chromosomes at the metaphase plate
5. Early anaphase- shortening of kinetochore microtubules
6. Telophase- de-condensation of chromosomes and surrounded by nuclear membranes, formation of cleavage furrow.
7. Cytokinesis- division of cytoplasm
Meiosis is a reductional cell division where the number of chromosomes
is divided into half. Gametes formations occur in animal cell and
meiosis is necessary for sexual reproduction which occurs in
eukaryotes. Meiosis influence stable sexual reproduction by halving of
ploidy or chromosome count. Without meiosis the fertilization would
result in zygote with twice the number of the parent.
Phases of meiosis include:
1. Meiosis I – separation of homologous chromosomes and production of two haploid cells (23 chromosomes, N in humans)
2. Prophase I – pairing of homologous chromosome pair and recombination (crossing over) occurs
3. Metaphase I – Homologous pairs move along the metaphase plate,
kinetochore microtubules from both centrioles attach to the homologous
chromosomes align along an equatorial plane.
4. Anaphase I – shortening of microtubules, pulling of chromosomes toward opposing poles, forming two haploid sets
5. Telophase I – arrival of chromosomes to the poles with each daughter cell containing half the number of chromosomes
6. Meiosis II – second part of the meiotic process with the production of four haploid cells from the two haploid cells
