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==Cell Division==
[[Image:Historic_1882_mitosis_drawing.jpg|thumb|Historic drawing of mitosis]]
* [http://www.nature.com/celldivision/milestones/index.html Cell Division Milestones], Recent Nobel Prizes

'''Features Two Mechanical Processes'''
* Mitosis - microtubule based segregation of chromosomes and formation of 2 nuclei
* Cytokinesis - microfilament based splitting of the cell cytoplasmic contents as a whole into 2 daughter cells

'''Features Two Types'''
* Mitosis - occurs in all cells, producing genetically identical progeny.
* Meiosis - occurs only in germ cells (sperm=spermatozoa and egg=oocyte), producing genetically different progeny.
** progeny = daughter cells, offspring

===Cell Changes===
Nucleus
* Chromosome condensation
* Nuclear envelope breakdown

Cytoplasm
* Cytoskeleton reorganization
* Spindle formation (microtubule, MT) Contractile ring (microfilament, MF)
* Organelle redistribution
==Mitosis==
{|
| Mitosis Movie<ref><pubmed>12105179</pubmed></ref> See also [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mcb.figgrp.5500 MCB Movie - The stages of mitosis and cytokinesis in an animal cell]

* Based on light microscopy of living cells light and electron microscopy of fixed and stained cells
* '''5 Phases''' - prophase, prometaphase, metaphase, anaphase, and telophase
* Cytokinesis 6th stage overlaps the end of mitosis

Note that DNA duplication has occurred earlier in the S Phase of the cell cycle.

| valign="bottom"|{{Mitosis movie 1}}
|}

===1. Prophase ===
* Chromosome DNA has been earlier duplicated (S Phase)
* Chromosomes begin condensing
* Chromosome pairs (chromatids) held together at centromere
* Microtubules disassemble
* Mitotic spindle begins to form
* Prophase ends when nuclear envelope breaks down

===2. Prometaphase===

* Microtubules now enter nuclear region
* Nuclear envelope forms vesicles around mitotic spindle
* Kinetochores form on centromere attach to some MTs of spindle
* Prometaphase ends when chromosomes move to metaphase plate

[http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mcb.figgrp.5509 MCB Movie - Centromeric attachment of microtubules]

===3. Metaphase===
[[Image:Mitosis_-_Metaphase.jpg]]
[[Image:Mitosis_fl.jpg|thumb|Metaphase fluorescent image of Mitotic spindle and Chromosomes]]
* Kinetochore MTs align chromosomes in one midpoint plane
* Metaphase ends when sister kinetochores separate

===4. Anaphase===
* Separation of sister Kinetochores
* shortening of Kinetochore microtubules pulls chromosome to spindle pole
* Anaphase ends as nuclear envelope (membrane) begins to reform

===5. Telophase===

* Chromosomes arrive at spindle poles
* Kinetochore MTs lost
* Condensed chromosomes begin expanding
** Continues through cytokinesis

===Cytokinesis===
* Division of cytoplasmic contents
* Contractile ring forms at midpoint under membrane
* Microfilament ring Contracts forming cleavage furrow
* Eventually fully divides cytoplasm

=== Cell Organelles ===

* Mitochondria - Divide independently of cell mitosis, distributed into daughter cells
* Peroxisomes - localise at spindle poles
* Endoplasmic Reticulum - associated with the nuclear envelope vesicles.
* Golgi Apparatus- Golgi stack undergoes a continuous fragmentation process, fragments are distributed into daughter cells, then reassembled into new Golgi stacks

==Meiosis==
[[File:Mitosis and meiosis.jpg|800px]]
[[Image:Mitosis_meiosis1.jpg|thumb|Comparison of Mitosis and Meiosis]]
Meiosis Germ cell division (haploid)
* Reductive division generates the haploid gametes (egg, sperm)
* Each genetically distinct from the parent

* Genetic recombination (prophase 1)
** Exchanges portions of chromosomes maternal/paternal homologous pairs
* Independent assortment of paternal chromosomes (meiosis 1)

Homologous chromosomes pairing unique to meiosis

* Each chromosome duplicated and exists as attached sister chromatids before pairing occurs
* Genetic Recombination shown by chromosomes part red and part black
** chromosome pairing in meiosis involves crossing-over between homologous chromosomes

===Meiosis I and II===
* '''Meiosis I''' - separates the pairs of homologous chromosomes, reduces the cell from diploid to haploid.
* '''Meiosis II''' - separates each chromosome into two chromatids (chromosome behavior in meiosis II is like that of mitosis).

[http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=cooper.figgrp.2486 Figure 14.32. Comparison of meiosis and mitosis]

'''Prophase I''' - The homologous chromosomes pair and exchange DNA to form recombinant chromosomes.
Prophase I is divided into five phases:
# '''Leptotene''' - chromosomes start to condense.
# '''Zygotene''' - homologous chromosomes become closely associated (synapsis) to form pairs of chromosomes consisting of four chromatids (tetrads).
# '''Pachytene''' - crossing over between pairs of homologous chromosomes to form chiasmata (form between two nonsister chromatids at points where they have crossed over)
# '''Diplotene''' - homologous chromosomes begin to separate but remain attached by chiasmata.
# '''Diakinesis''' - homologous chromosomes continue to separate, and chiasmata move to the ends of the chromosomes.

'''Prometaphase I''' - Spindle apparatus formed, and chromosomes attached to spindle fibres by kinetochores.

'''Metaphase I''' - Homologous pairs of chromosomes (bivalents) arranged as a double row along the metaphase plate. The arrangement of the paired chromosomes with respect to the poles of the spindle apparatus is random along the metaphase plate. (This is a source of genetic variation through random assortment, as the paternal and maternal chromosomes in a homologous pair are similar but not identical. The number of possible arrangements is 2n, where n is the number of chromosomes in a haploid set. Human beings have 23 different chromosomes, so the number of possible combinations is 223, which is over 8 million.)

'''Anaphase I''' - The homologous chromosomes in each bivalent are separated and move to the opposite poles of the cell.

'''Telophase I''' - The chromosomes become diffuse and the nuclear membrane reforms.

'''Cytokinesis I''' - Cellular cytoplasmic division to form two new cells, followed by Meiosis II.

'''Prophase II''' - Chromosomes begin to condense, nuclear membrane breaks down and spindle forms.

'''Metaphase II''' - Spindle fibres attach to chromosomes, chromosomes align in cell centre.

'''Anaphase II''' - Chromosomes separate and move to the opposite poles of the cell.

'''Telophase II''' - Chromosomes reach spindle pole ends and the nuclear membrane reforms.

'''Cytokinesis''' - Cellular cytoplasmic division to form new cells.

===Comparison of Meiosis/Mitosis===
[http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio17.swf::Comparison%20of%20Meiosis%20and%20Mitosis McGraw-Hill Animation comparing Mitosis and Meiosis]
* After DNA replication 2 nuclear (and cell) divisions required to produce haploid gametes
* Each diploid cell in meiosis produces 4 haploid cells (sperm) 1 haploid cell (egg)
* Each diploid cell mitosis produces 2 diploid cells

Talk:ANAT2341 Lab 1 - Gametogenesis - Revision history

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