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Cell Division: Mitosis & Meiosis
Cell Division
All new cells come from previously existing cells. New cells are formed by the process of cell division, which involves both replication of the cell's nucleus (karyokinesis) and division of the cytoplasm (cytokinesis).
Cell Division
Cell division is a process by which a parent cell divides into two or more daughter cells.
It is the process by which we grow and it is how our body repairs and renews itself.
Cell division is of three types: Amitosis Mitosis Meiosis
Binary Fission/ AmitosisBinary Fission/ Amitosis
Most cells reproduce through Most cells reproduce through some sort of Cell Divisionsome sort of Cell Division Prokaryotic cells divide through a simple form of division Prokaryotic cells divide through a simple form of division
calledcalled Binary FissionBinary Fission
3 step process:3 step process:
1. Single “naked” strand splits and forms a duplicate of 1. Single “naked” strand splits and forms a duplicate of itself.itself.
2. The two copies move to opposite sides of the cell2. The two copies move to opposite sides of the cell
3. Cell “pinches” into two new and identical cells called 3. Cell “pinches” into two new and identical cells called ""daughter cells". (Cell wall then forms if applicable) (Cell wall then forms if applicable)
Eukaryotic ChromosomeEukaryotic Chromosome
Mitotic SpindleMitotic Spindle
Cell Cycle Occurs between one cell
division & next. Three main stages –
interphase, mitosis & cytokinesis.
Interphase – encompasses G1, S & G2 phases is the period of synthesis & growth.
Mitosis – contains prophase, metaphase, anaphase & telophase.
Cytokinesis – division of cytoplasm.
Interphase
Encompass stages G1, S & G2
G1 – growth stage
S – synthesis stage
G2 – time between DNA
Synthesis & Mitosis
Each chromosome exists as a
pair of chromatids joined together
by a centromere.
Mitosis Cell Division Mitosis: Two daughter cells
form,
contain same Number of chromosomes as mother cell
Contains four phases: Prophase Metaphase Anaphase Telophase
Prophase
Nuclear membrane disintegrates Nuclelous disappears Chromosomes condense Chromatids joined at centromere Centrioles begin migration to
poles Mitotic spindle begins to form
between centrioles Kinetochores begin to mature
and attach to spindle
Metaphase
Kinetochores attach chromosomes to mitotic spindle
Chromosomes are align along the metaphase plate
Spindle fibers are now clearly visible
Anaphase
Kinetochore microtubules shorten Resulting in separation of
chromosomes to opposite poles Polar microtubules elongate, preparing
cell for cytokinesis
Telophase Nuclear envelope forms Nuclear envelope forms
around both sets of around both sets of chromosomeschromosomes
DNA uncoilsDNA uncoils Spindle & Astral fibers Spindle & Astral fibers
completely disappear completely disappear
CytokinesisCytokinesis
Cytokinesis happens with most (but not all) Cytokinesis happens with most (but not all) cellscells
Cytoplasm & organelles move (mostly equally) Cytoplasm & organelles move (mostly equally) to either side of the cell. Cell Membrane to either side of the cell. Cell Membrane “pinches” to form 2 separate cells“pinches” to form 2 separate cells
Animal Cytokeneisis
Cytokenesis differs significantly between Animal & Plant cells.
With animals, the membranes pinch together to form a cleavage furrow, which eventually fuses to form two daughter cells
Plant Cytokinesis
With Plants, a cell wall must be formed between the 2 daughter cells.
Vesicles containing Cellulose form and fuse between the two daughter cells, eventually forming a complete cell wall.
Significance of Mitosis
Genetic stability (In mitosis, the two cells will each be genetically the same. )
Growth Cell replacement Regeneration Asexual reproduction
Mitosis produces genetically identical cells whereas meiosis does not.
Meiosis Cell Division
Meiosis: Reduces two sets of chromosomes to one set in
daughter cell.
Meiosis is a two-part cell division process Meiosis I – Reduction Meiosis II – Division
Results in 4 cells with 1/2 the normal genetic information
Meiosis I
Consist of four stages Prophase I Metaphase I Anaphase I Telophase I
Prophase I
Homologous chromosomes further condense and pair Crossing-over occurs Spindle fibers form between centrioles Spindle fibers move towards opposite poles
Crossing Over
Segments of homologous chromosomes break and reform at similar locations.
Metaphase I
Microtuble spindle attaches to chromosomes Homologus pairs align align equator
Anaphase I
Homologus pairs of chromosomes separate Pairs move to opposite poles
Telophase I
One set of paired chromosomes arrives at each pole Nuclear division begins Nuclear membrane re-forms
Meiosis II
Consist of four stages Prophase II Metaphase II Anaphase II Telophase II
Prophase II Chromosomes recondense Spindle fibers form between centrioles Spindle fibers move towards opposite poles
Metaphase II
Microtuble spindle apparatus attaches to chromosomes Chromosomes align along spindle
Anaphase II
Sister chromatids separate Chromatids move to opposite poles
Telophase II
Chromatids arrive at each pole
Cell division begins
Significance Of Meiosis Produce the gametes in sexually reproduce
organism. Meiosis reduces the chromosome number by half,
enabling sexual recombination to occur. Meiosis of diploid cells produces haploid
daughter cells, which may function as gametes. Gametes undergo fertilization, restoring the
diploid number of chromosomes in the zygote Restore the diploid number in genome.
produces haploid gametes so that the diploid number of the species remains constant generation after generation.
Increase genetic variation in population.
Significance Of Meiosis
Sexual reproduction Genetic variation
Comparison between Mitosis and Meiosis
Mitosis Meiosis
Occurs in somatic cells Occurs in reproductive cells.
One single division of the mother cell. Two divisions of the mother cell.
Chromosome number remains same Chromosome number become halves
A mitotic mother cell can be either diploid
A meiotic mother cell is always haploid
Two diploid daughter cells Four haploid daughter cells
Genetically identical Genetically different
Crossing over does not occur
No kiasma forms in this cell division.
Nucleus and chromosome both are divided once.
Usually simple
Occurs crossing over
Occurrence of kiasma usually takes place.
Nucleus is divided for two times but the chromosome is divided for once
Usually complex
Comparison of Mitosis & Meiosis
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