Angela.Bang-Ji

Comparison of mitosis and meiosis

What is mitosis and meiosis Meiosis – cell division that results in cells

that have half the normal chromosome number(haploid gametes), it is also called reduction division, specific to create sex cells.

Mitosis – Cell division that results in identical cells, used for growth and repair of organisms.

Cell Cycle : Growth Stage/InterphaseGrowth stage also called interphase is

where the cell carries out its regular metabolic function and prepares for its next division

Interphase is divided into three phases : G1 phase, S phase and G2 phase.

By the end of interphase, the cell is ready to begins the process of nuclear division: mitosis.

Three phases in InterphaseG1 phase (Growth 1) – The cell goes through rapid

growth and metabolic activities. S phase (Synthesis) – The middle stage of

interphase where the cell’s DNA is copied exactly. Which means that the chromatin replicates to create a second identical set of DNA. After the replication, the two identical chromosomes – sister chromatids – are joined at the centromere

G2 phase (Growth 2) – During the replication in S phase, the cell consumed a large amount of energy, therefore this stage allow the cell to regenerate energy for division. As well, the cell manufactures proteins and other molecules to make structures required for division of the nucleus and cell.

Sister chromatids are joined by the centromere

Diagrams

DNA repilcation occur during S phase

Cell division : MitosisFour phases in the process of mitosis -

Prophase, Metaphase, Anaphase, and Telophase

After the cell has been through all the phases, it enter cytokinesis - the division of the cytoplasm and the organelles into two separate cells.

Mitosis : Prophase Prophase - During this phase, the chromatin condenses

into tightly pack chromosomes while the nuclear membrane breaks down, releasing chromosomes into the cytoplasm.

As the nucleolus disppears, pair of cylndrical organelles called centrioles move their way to the opposte poles of the cell

During the separation of the centrioles, a network fibres called the spindle apparatus forms between them

Prophase : Diagrams

Spindle fibre is made of microtubules - hollow tubes of proten that facilitate movement of chromosomes within a cell

Mitosis : MetaphaseDuring metaphse, the spindle fibres guide

the chromosomes to the centre line of the cell and attach to the centromere of each chromosome.

The chromosomes are lined up in such way that one sister chromatid face one pole and the other sister chromatid face the opposite pole.

Metaphase : Diagrams

The chromosomes are lined up horinzontally by the spindle fibres

Mitosis : Anaphase Before anaphase, the chromosomes are line up at the

centre line of the cell. During anaphase, the centromere splits apart and the sister chromatids separate from one another.

The spindle fibres from each end still attach to the split centromere, it shortens and pulls the sister chromatid towards its pole.

At the same time, microtubules in the spindle apparatus lengthen and force the poles of the cell away from one another

By the end of anaphase, one complete diploid set of chromosomes has been gathered at each pole and the process of lengthening the microtubules result in a elongated cell

Anaphase : Diagrams

Notice the elongated cell

Mitosis : TelophaseFinal phase of mitosisThe chromatids begin to unwind into longer

and less visible strands of chromatin at the opposite pole of the cell

The spindle fibres begin to break downNuclear membrane starts to form around

each new set of chromosomes and a nucleolus forms within each new nucleus

Telophase : Diagrams

Nuclear membranes are formed The cell will now enter Cytokinesis

CytokinesisThis is the last step of cell division,

interphase and mitosis are the process of nuclear division, Cytokinesis is the division of the cytoplasm to complete the creation of two new daughter cells.

In animal cells, an indentation forms in the cell membrane along the cell equator, the indentation deepens until the cell is pinched in two.

This result in the equal divison of the cytoplasm and organelles between the two halves of the cell

Cytokinesis : Diagrams

Indentation at the equator

Two daughter cells are formed

End of cell division, the daughter cells are now in G1 phase

MeiosisOther form of cell division is called Meiosis,

the process that produces haploid gametes from diploid cells in the ovaries and testes - sex cells -

Two main parts to Meiosis : Reduction division and Recombination

During Meiosis, the four phases that occur in mitosis happens twice, therefore it is called Meiosis I and Meiosis II.

Interphase before MeiosisLike somatic cells, germ cells also goes

through the growth and synthesis phases before dividing

Duplicated chromosomes are formed by the end of interphase

Meiosis : Prophase IThe homologous chromosomes which

contains the same genes but carry different alleles of these genes are align side by side in the this phase.

The alignment of the homologous chromosomes are called synapsis

At synapsis, homologous non-sister chromatids lie side by side. This is a important step that will be later demonstrated in genetic recombination

Prophase I : Diagrams

Crossing over between non-siser chromatids may occur. This increases variation in gametes and offspring

Metaphase IA spindle fibre attach to the centromere of

each chromosomeA spindle fibre from one pole attaches to

one pair of sister chromatids in the tetrad, and a spindle fibre from the opposite pole attach to the other pair of sister chromatids

The spindle fibres guide each tetrad to the equator of the cell, however the chromosomes do not line up in single file as they do in mitosis, instead they line up as homologous pairs.

Metaphase 1 : Diagrams

chromosomes line up as homologous pairs.

Anaphase ISimilar to Mitosis, during anaphase I in

Meiosis, the spindle fibres shorten cause the homologous chromosomes to separate from one another, making their way to opposite poles of the cell

Since the sister chromatids are still held together, the centromeres do not spilt

This result in a single chromosome - made up of two sister chromatids - from each homologous pair moves toward the poles.

Anaphase 1 : Diagrams

Result in a single chromosome - made up of two sister chromatids

Telophase IThe homologous chromosomes begin to

uncoil and the spindle fibres disappear

Each new cell contains one set of sister chromatids and is now haploid

Meiosis IIBy the end of telophase I, new cells

contains one set of sister chromatids are formed and is now haploid

Chromosome replication does not take place before the next phase of meiosis

The process of Meiosis II are similar to the phases of mitosis

Each cell that enters meiosis II is haploid but consists of replicated chromosomes.

At the end of meiosis II, the daughter cells are still haploid but they contain single unreplicated chromosomes.

Meiosis II : Diagrams

daughter cells are still haploid but they contain single unreplicated chromosomes.

Similarities between Mitosis and MeiosisBoth process go through chromosome

replicationMeiosis II is similar to MitosisBoth Mitosis and Meiosis go through

interphase,prophase,metaphase,anaphase and telophase

Both use spndle fibers to separate chromatids from each other

Differences between Mitosis and MeiosisMitosis produce identical cells, Meiosis produce 4

daughter cells are haploid but they contain single unreplicated chromosomes.

Mitosis is used for growth and repair of organisms, Meiosis is used to reproduce gametes

Four phases in Meiosis I is different from Mitosis, in prophase I synapsis happen, in metaphase I crhomosomes line up as homologous pairs, in anaphase I centromeres do not split result in single chromosome from each homologous pair moves to each pole of the cell, in telophase I daughter cell contain one set of sister chromatid

References http://cyberbridge.mcb.harvard.edu/mitosis_4.html http://mrsmaineswiki.wikispaces.com/file/view/

Prophase_thing_emily.png/34094393/Prophase_thing_emily.png http://fifieyy.blogspot.ca/2013/10/mitosis-type-of-cell-division.html http://www.dkimages.com/discover/previews/801/908016.JPG http://www.tutorvista.com/biology/cytokinesis-pictures http://iws.collin.edu/biopage/faculty/mcculloch/1406/outlines/chapter

%2012/Ar14-11a.JPG http://www.phschool.com/science/biology_place/biocoach/images/

meiosis/meana1.gif

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