Comparing mitosis and meiosis (video)

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Comparing mitosis and meiosis

Mitosis	Meiosis
Prophase	Prophase  1
Metaphase	Metaphase   1
Anaphase	Anaphase 1
Telophase	Telophase 1
	No Interphase, no replication of DNA
	Prophase 2
	Metaphase 2
	Anaphase 2
	Telophase 2

How a cell cycle works

MITOSIS & CYTOKINESIS

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Prophase
• The chromosomes in the nucleus condense and become more tightly coiled.
• Each chromosome now consists of a pair of sister chromatids joined together at the centromere.
• In the cytoplasm, the spindle fibres begin to form and extend between the centrioles.
• Each pair of centrioles then migrates to lie at the opposite poles of the cell. The chromatids are attached to the fibres of the spindle by their centromeres.
• At the end of prophase, the nucleolus disappears and the nuclear membrane disintegrates.

Metaphase
• Metaphase begins when the centromeres of all the chromosomes are lined up on the metaphase plate, an imaginary plane across the middle of the cell.
• The mitotic spindle is now fully formed.
• The two sister chromatids are still attached to one another at the centromere.
• Metaphase ends when the centromere divide.

Anaphase
• During anaphase, the two sister chromatids of each chromosome separate at the centromere.
• The sister chromatids are pulled apart to the opposite poles by the shortening of the spindle fibres.
• Once separated, the chromatids are referred to as daughter chromosomes.
• By the end of anaphase, the two poles of the cell have complete and equivalent sets of chromosomes.

Telophase
• Begins when the two sets of chromosomes reach the opposite poles of the cell.
• The chromosomes start to uncoil and revert to their extended state (chromatin).
• The chromosomes become less visible under the microscope.
• The spindle fibres disappear and a new nuclear membrane forms around each set of chromosomes.
• The nucleolus also reforms in each nucleus.
• The process of mitosis is now completed.

When chromosomes fail to separate

Example of Meiotic Nondisjunction that causes disease like Down Syndrome

How meiosis work?

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http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html

Stages of meiosis

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter3/animation__stages_of_meiosis.html
MEIOSIS I
Prophase I
• The chromosomes begin to condense. They become shorter, thicker and clearly visible.
• The homologous chromosomes come together to form bivalent through a process called synapsis.
• Non-sister chromatids exchange segments of DNA in a process known as crossing over.
• Crossing over results in a new combination of genes on a chromosome.
• The points at which segments of chromatids cross over are called chiasmata.
• At the end of prophase I, the nucleolus and nuclear membrane disappear.
• The two pairs of centrioles migrate to the opposite poles of the cells.
• These features are similar to those of prophase during mitosis.
Metaphase I
• The chromosomes are lined up side by side as tetrads on the metaphase plate.
• The chromosomes are still in homologue pairs.
• The centromere does not divide.
Anaphase I
• The spindle fibres pull the homologous chromosomes away from one another and move them to the opposite poles of the cell.
• Each chromosome still consists of two sister chromatids which move as a single unit.
• Although the cell started with four chromosomes, only two chromosomes (each with two sister chromatids) move towards each pole.
Telophase I
• The chromosomes arrive at the poles.
• Each pole now has a haploid daughter nucleus because it contains only one set of chromosomes.
• The spindle fibres disappear.
• The nuclear membrane reappears to surround each set of chromosomes.
• The nucleolus then reappears in each nucleus.
Cytokinesis
• Cytokinesis usually occurs simultaneously with Telophase I, resulting in two haploid daughter cells, each receiving one chromosome from the homologous pair.
• Meiosis II follows immediately after cytokinesis, usually with no interphase between them.
• DNA replication does not occur and the chromosomes remain in a condensed state.
MEIOSIS II
Prophase II
• The nuclear membranes of the daughter cells disintegrate again.
• The spindle fibres reform in each daughter cell.
Metaphase II
• The chromosomes, each still made up of sister chromatids, are positioned randomly on the metaphase plate with the sister chromatids of each chromosome pointing towards the opposite poles.
• Each sister chromatid is attached to the spindle fibres at the centromere.
Anaphase II
• The centromere of the sister chromatids finally separate, and the sister chromatids of each chromosome are now individual chromosomes.
• The chromosomes move towards the opposite poles of the cell.
Telophase II
• Finally, the nucleolus and nuclear membranes reform. The spindle fibres break down.
• Cytokinesis follows and four haploid daughter cells are formed, each containing half the number of chromosomes and is genetically different from the parent diploid cell.
• These haploid cells (n) will develop into gametes.

Cytokinesis in animal and plant cell

How cancer develops - Uncontrolled cell division

This video demonstrates how cancer growth happens in human body. It is due to uncontrolled cell division.

Cloning Of Dolly, the sheep

Tissue culture

Step 1: Weigh out 2.5 g of nutrient agar and add to 250 ml of distilled water.
Step 2 : Then add hormone into the agar solution. Heat and stir until the agar dissolves.
Step 3 :Pour the hot nutrient agar into several test tubes about 5 cm3 in height.
Allow the agar to cool and solidify in each test tube.
Step 4 :Germinate some mustard seed in a warm lighted place until the cotyledon starts to unfold.
Step 5 : Cut the tips of the seedling just above the shoot apex (meristem).These tissues are called explants.
Step 6 : Put one explant in each test tube.
Step 7 : Cover the tubes with a cling film and place the tubes into a rack by the window.
Step 8 : The tissue cells are left to divide by mitosis to produce a mass of loosely arranged and undifferentiated cells called callus. The callus will then grow into plantlets(little plants) which will grow into adult plants.

When chromosomes fail to separate

Example of Meiotic Nondisjunction that causes disease like Down Syndrome

Answers to Hands on Pg 50

Section B
3a) Meiosis is a process of cell division producing gametes which are haploid (n) as compared to the parent cell which is diploid (2n).
b)

A chromosome consists of 2 chromatids held together at the centromere.

Paring of homologous chromosomes occurs

Crossing over takes place.

Nuclear membrane and nucleolus disappear.

c)

MITOSIS	MEIOSIS
Takes place in somatic cells	Takes place in reproductive cells
Produce new cells for growth or tissue repair.	Produce gametes
Involves one division only in one cycle	Involves two divisions in one cycle
No pairing of homologous chromosomes	Pairing of homologous chromosomes during Prophase I
Crossing over does not occur	Crossing over occurs during Prophase I
2 diploid cells are produced	4 haploid cells are produced
The number of chromosomes in a daughter cell is the same as its parent cell	The number of chromosomes in a daughter cell is the halvedof its parent cell
The daughter cells are identical to the parent cell	The daughter cells are not identical to the parent cell and to each other

4a) Process of cell division is mitosis.

Preparatory stage is interphase.

Interphase

· Replication of DNA

· Storage of energy

· More organelles are produced

· Mitosis consist of prophase, metaphase, anaphase and telophase

Prophase

· Chromosomes thicken and shortens

· Each chromosomes consists of 2 chromatids

· Nuclear membrane and nucleolus starts to disappear

Metaphase

· Chromosomes are arranged in a line across the middle of the cell

· Centrosomes are held by spindle fibre

Anaphase

· Centromeres of chromosomes divide into 2.
· Chromatids are separated and pulled to the opposite poles of the cell.

Telophase

· Spindle fibres disappear

· Nuclear membrane reappear

· Chromosomes are seen as fine threads

. Formation of cell plates begin

b) Tissue culture can be used to produce more seedlings.

Small pieces of meristem tissue/explant are removed from a parent plant and cut it into small pieces.
Sterilise the pieces of tissues with dilute sodium hypochlorite solution.
Place each sterile tissue onto a culture medium containing nutrients and growth hormone.
The tissue cells are left to divide by mitosis to produce a mass of loosely arranged and undifferentiated cells called callus.
The callus is then stimulated with shoot stimulating hormones to form multiple shoots.
Separate the shoots in nutrient medium with root stimulating hormones to encourage rooting.
Once the roots grow, the plantlets (little plants) are planted in sterile soil to grow into adult plants.