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)

Cell division:

a) Mitosis (2n 2n) (1 parent cell 2 daughter cells)

b) Meiosis (2n n) (1 parent cell 4 daughter cells)

Chromatid

Chromosome

Chromosome

Homologous Chromosome

Sister Chromatid

Mitosis (somatic cells)

1 parent cell (2n) 2 daughter cells (2n)

Interphase Mitosis Cytokinesis

Interphase is divided into:a)G1 – growth of cell by producing proteins and organellesb) S – synthesis of DNA (thread-like chromatin)c) G2 – growth of cell by producing proteins and organelles

Mitosis is divided into:

a)Prophaseb)Metaphasec) Anaphased)Telophase

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

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

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