Chap 5
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Transcript of Chap 5
Chap 5Cell Division
Terms to take note and remember!!
Haploid – Cells with single unpaired set of chromosome (n)
Diploid – Cells with two sets of chromosome (2n)
Chromatid
Sister chromati
d
Chromosome
Homologous chromosome
Chromosome
Cell division:
a)Mitosis (2n 2n) (1 parent cell 2 identical daughter cells)
b)Meiosis (2n n) (1 parent cell 4 different daughter cells)
Mitosis Meiosis
Mitosis (somatic cells)
1 parent cell (2n) 2 identical daughter cells (2n)
Interphase Mitosis CytokinesisCell cycle
1 parent cell (2n)
2 identical daughter cells (2N)
G1 phaseGrowth of cell before DNA duplicates
S phaseDNA duplicates
G2 phaseGrowth of cell after DNA duplicates
Cytokinesis
Cell cycle
Mitosis
Prophase
Chromosomes start to appear and condense as 2 identical chromatids
Nuclear membrane breaks down and nucleolus disappear.
Centrioles move apart to opposite poles
Spindle fibre begins to form
Metaphase
Chromosomes move to cell’s equator
Chromosomes line up along the equator with centromeres attached to spindle fibre
Each chromatid faces it’s own pole
Anaphase
Chromosome divides into two Each sister chromatids separate
and move to opposite poles When the chromatids reached its
own pole, they become independent chromosomes
Telophase There are now 2 sets of chromosomes, one at each pole
Chromosomes become thread-like structures
Spindle fibre disappear Nuclear membrane begins to
form around both sets of chromosomes
Nucleolus reappears Cytokinesis begins
Cytokinesis
Animal cells
Plant cells
cleavage
Cell plate
Cell cycle
http://www.youtube.com/watch?v=VGV3fv-uZYI
Regulation and application of mitosis
a) Repair damaged cells and replace dead cellsb) Tissue culturec) Clonningd) Cancer (uncontrolled mitosis)
Importance of mitosis
a) Repair damaged cells and replace dead cellsb) Asexual reproduction in unicellular organismsc) Preserve diploid number of chromosomesd) Ensure new cells are identical to parent cells
Meiosis (reproductive cells)
1 parent cell (2n) 4 daughter cells (n)
Meiosis is divided into:a)Meiosis I
Prophase I Metaphase I Anaphase I Telophase I
b) Meiosis II Prophase II Metaphase II Anaphase II Telophase II
Same as
mitosis
1 parent cell (2n)
4 different daughter cells (n)
Prophase I Chromosomes thicken and condense
Each chromosome consists of 2 sister chromatids
Homologous chromosomes pair together (bivalent) via synapsis.
The criss-cross between homologous chromosomes are known as chiasmata
This results in genetic variation Centrioles move to opposite
poles Spindle fibre forms Nuclear membrane and nucleolus
disintegrate Paired homologous chromosomes
line up at equator of the cell Each chromosome are attached to
spindle fibre at centromere Each chromosome faces each own
pole
Metaphase I
Prophase I Chromosomes thicken and condense
Each chromosome consists of 2 sister chromatids
Homologous chromosomes pair together (bivalent) via synapsis.
The criss-cross between homologous chromosomes are known as chiasmata
This results in genetic variation Centrioles move to opposite
poles Spindle fibre forms Nuclear membrane and nucleolus
disintegrate Paired homologous chromosomes
line up at equator of the cell Each chromosome are attached to
spindle fibre at centromere Each chromosome faces each own
pole
Metaphase I
Homologous chromosome undergoing synapsis
Chiasmata
Anaphase I
Paired homologous chromosomes separate from one another and move to opposite pole
Telophase I Chromosomes reached their own pole
Each pole has haploid chromosome set
Spindle fibre disappear Nuclear membranes and nuclei
reform Cytokinesis begins
http://www.youtube.com/watch?v=kVMb4Js99tAVideo of
meiosis
Importance of meiosis
a)Allow trait inheritance in offspringb)Maintain diploid number in each generationc) Ensure production of haploid gametes in sexual
reproductiond)Produce genetic variation
Comparison between Meiosis I and II
Meiosis I Meiosis II
Similarities1. Consists of 4 stages, ie. prophase, metaphase, anaphase and telophase2. Involves division of nucleus and cytoplasm
DifferencesSynapsis occur No synapsis
Crossing over occurs No crossing over
In metaphase I, paired homologous chromosomes line up at equator
In metaphase II, sister chromatids line up at equator
In anaphase I, paired homologous chromosomes separate and move to opposite poles
In anaphase II, sister chromatids separate and move to opposite poles
At the end of meiosis I, 2 haploid cells are formed
At the end of meiosis II, 4 haploid cells are formed
Meiosis Mitosis
Similarities1. Both process are cell division of cells2. Chromosomes only replicate once
Differences
AspectsReproductive organs (testes & ovary)
Place occur In somatic cells
Parent cell divides twice No. of division Parent cells divides once
4 haploid (n) daughter cells No. of daughter cells 2 diploid (2n) daughter cells
Synapsis occur in prophase I Synapsis No synapsis
Twice No. of cytokinesis Once
Crossing over in prophase I Crossing over No crossing over
Each daughter cell has ½ the no. of chromosome of parent cell
No. of chromosome in daughter cell
Each daughter cell has the same no. of chromosome as parent cell
Comparison between Meiosis and Mitosis
Differences
AspectsGenetic composition are not identical to parent cell or to each other
Genetic composition of daughter cells
Daughter cells are genetically identical to parent cell and each other
Occurs during interphase before Meiosis I begins
DNA replication Occurs during interphase before mitosis begins
Produce gametes, causing genetic variation, reduce no. of chromosome into half
Role in animal body Produce cells for growth, maintenance and repair body tissues