Biology

Mitosis maintains ploidy level, while meiosis reduces it. Meiosis may be considered a reduction phase followed by a slightly altered mitosis. Meiosis occurs in a relative few cells of a multicellular organism, while mitosis is more common.

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meiosis is more complicated than mitosis

actually mitosis is a part of mitotic cell division by definition
meiosis is a part of meiotic cell division by definition
but simply and collectively, mitosis~mitotic cell division, meiosis~meiotic cell division

mitosis involves the production of new genetically identical cells
meiosis involves the production of gametes

step of mitotic cell division
1)chromosomes replicate
2)chromosomes appear visible like "X", ie w/2 chromatids
3)nuclear membrane disintegrates
4)chromosomes line up at equator
5)spindle fibre pull chromatids towards the poles
6)formation of nuclear membrane around 2set of chromosomes
7)chromosomes appear invisible
8)cell membrane constricts and cytoplasm is divided(animal cells)
formation of new cell walls and cell membranes between nuclei(plant cells)

step of meiotic cell division
1)chromosomes replicate
2)chromosomes shorten and thicken and appear visible as small threads
3)homologous chromosomes pair up
4)nuclear membrane disintegrates, chromosomes appear w/2 chromatids
4)homologous chromosomes line up at equator in pairs
5)spindle fibre pull homologous chromosomes towards the poles(E-W direction)
ie homologous chromosomes members separate from each other
6)formation of nuclear membrane around 2 haploid set of chromosomes
7)nuclear membrane disintegrates
8)chromosomes line up at equator
9)spindle fibre pull chromatids towards the poles(N-S direction)
10)formation of nuclear membrane around 4 haploid set of chromosomes
11)chromosomes uncoil and appear invisible
12)cytoplasm divides and formation of new cell membranes

significance
For mitotic cell division, formation of new cells which are genetically identical is important for growth and repair in most organisms, and asexual reproduction of some organisms like amoeba

For meiotic cell division, formation of haploid gametes can ensure that after fertilization, the diploid number of chromosomes can be restored in a zygote, so that number of chromosomes will not increase exponentially from generations to generations.
Also, as separation of homologous chromosomes are indempendent from each other in step 5(independent assortment), different genetic combination(in human, there are total 2^23 combinations) occurs among formed gametes, ie genetic variations occur after formation of zygote(2 gamtes combined, total combinations=2^46 in human), this allows species to survive throughout time by the principle"survival of the fittest" whenever the species is in changing environmental conditions.

2007-01-28 01:21:59 補充：
Use example of human(46 chromosomes)In mitotic cell division, new cells formed have 46chromosomesIn meiotic cell division, new cells formed have 23chromosomes