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CELL DIVISION. By Fulden Donangil. Figure 1. Types of Cell Division:. 1-Mitosis 2-Meiosis. MITOSIS. Mitosis is a kind of cell divison which occurs in somatic cells and results in two daughter cells. - PowerPoint PPT Presentation
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CELL DIVISION By Fulden Donangil
Figure 1
Types of Cell Division:
1-Mitosis
2-Meiosis
MITOSIS Mitosis is a kind of cell divison which occurs in somatic
cells and results in two daughter cells.
These daughter cells are identical to each other and to the parent cell.
Daughter cells are diploid which means that they they have 2 sets of chromosomes.
One set of chromosomes is donated from the mother and the other set of chromosome donated from father.
There are 5 stages of Mitosis
1-Interphase
2-Prophase
3-Metaphase
4-Anaphase
5-Telophase Figure 2
Interphase There are 3 stages in
interphase;
-G1: The cells grow and get bigger for the division.
-S : DNA is synthesized by the process of DNA Replication.
-G2 : Mitochondria and other organelles divide.
Figure 3
Prophase Chromosomes become
shorter and fatter.
They move to opposite poles of the cell and spindle fibres are formed.
Nucleolus disappears.
Nuclear membrane breaks down Figure 4
Metaphase Chromosomes line up at
the equator individually.
Spindle fibers attach to chromosomes at the centromere.
Figure 5
Anaphase Spindle fibres pull
chromosomes apart.
Microtubules shortening.
Centromere of each chromosomes breaks down.
Daughter chromosomes travels to opposite poles.
Figure 6
Telophase All chromosomes are at
opposite poles.
Spindle fibres break down.
Nuclear envelope reformed.
Chromosomes become invisible. Figure 7
Animation of Mitosishttp://www.cellsalive.com/mitosis.htm
MEIOSIS Meiosis is a kind of cell division which occurs in
gametes(sperms and eggs) and results in four daughter cells.
Daughter cells are genetically different from each other and from parent cells.
Daughter cells are haploid which means that they have one complete set of chromosomes.
During meiosis DNA replicates once but the nucleus divides twice. Therefore two division occur in meiosis.
Importance of Meiosis It halves the chromosome number.
It is important to have a diploid cell with correct number of chromosome(46 chromosome).
It increases variation.
First Division of Meiosis Prophase 1
Metaphase 1
Anaphase 1
Telophase 1
Prophase 1 Most of the steps are same
as in the mitosis except;
Homologous chromosomes pair up to from bivalent consisting of 4 chromatids.
Two chromosomes can overlap with each other which is known as CROSSING OVER.
Metaphase 1 Most of the steps are
same as mitosis except;
Spindle fibres move bivalent chromosomes to line up at the equator instead of single chromosomes.
Anaphase 1 The centromeres do not divide
One chromosome from each homologous pair moves to each end of the cell.
As a result, the chromosome number in each cell is half of the original.
Telophase 1 All of the steps are same
as mitosis except;
Whole chromosome is produced instead of one sister chromatid.
Second Division of Meiosis The second division of meiosis is
completely the same as mitosis.
However at the end of Meiosis, 4 daughter cells each with half of the chromosome number of the original diploid cell are formed.
Stages of Second Division
Prophase 2 Metaphase 2 Anaphase 2
Telophase 2
Animation of Meiosishttp://www.cellsalive.com/meiosis.htm
Questions 5 differences between mitosis and
meiosisMITOSIS MEIOSIS
2 daughter cells formed 4 daughter cells formed
Occurs in body cells Occurs in gametes
Daughter cells are diploid Daughter cells are haploid
Daughter cells are identical to each other
Daughter cells are different from each other
No crossing over of chromosomes
Crossing over of chromosomes in prophase 1
Questions(a) (i) The diagrams show some of the stages of mitosis. Arrange the letters A - D to give the correct sequence of stages.
Sequence D A C B
(ii) Describe the role of the spindle in mitosis:
(b) Sexual reproduction involves the fusion of gametes. Explain the importance of meiosis in the life cycle of a sexually reproducing organism.
It attaches centromeres and seperates the daughter chromatids.
Meiosis halves the chromosome number and increase the variation.
References Edexcel AS Biology, A Pearson
Company, 2008, page 148,149,150,158,159
Richard Llopis Garcia’s CD
THE END