purposes of cell division -...
TRANSCRIPT
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Purposes of Cell Division
Increase the number of cells for growth and repair of worn out tissues What examples in the human body can you
think of? Transmit genetic information to later
generations Why do you think this is important?
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Whether for growth or reproduction, all cell division types rely on the brain of the cell... the NUCLEUS The nucleus contains the most important
parts of the cell with regards to genetics the CHROMOSOMES
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nucleus chromosome
chromatins
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What is a chromosome?
Genetic material found inside the nucleus of a cell.
Made of protein and DNA, bound together and wound up.
DNA contains the genetic information (blueprint) of an organism.
Each organism in a species has unique DNA, made up of genes.
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chromosome
gene controlling skin colour
A gene is a short length of DNA on a chromosome which controls an inherited character of the organism
gene controlling tongue rolling
gene controlling eye colour
gene controlling blood group
A chromosome carries a lot of genes
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Each species has a fixed number of chromosomes in the nucleus of each of its cells Chromosomes always exist in pairs in the
body (somatic) cells. These are called
Each human somatic cell has 46 chromosomes 23 pairs of homologous chromosomes
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Members of homologous chromosomes carry same genes
But the genes on the members of homologous chromosomes may be of different forms.
Each form of a gene on each chromosome is called an allele.
allele for brown skin colour gene for skin colour
allele for white skin colour gene for skin colour
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Alternative forms of genes on the same position of the homologous chromosomes which control the same character but have different expressions
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One homologous chromosome comes from your mother and one comes from your father. So your father might have given you the allele for blue eyes while your mother gave you the allele for brown eyes.
However, the combination of the alleles allows for variation in the offspring.
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22 pairs are identical in both sexes autosomes
The 23rd pair is different in male and female sex chromosomes
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Chromosome Number
Each species has a unique number of chromosomes. In humans the full compliment chromosome
number is 46. Each somatic cell contains 46 chromosomes
and are called diploid (2n). Each gamete contains 23 chromosomes and
are called haploid (n)
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Steps of cell division
Although there are more than 2 steps, essentially cell division is grouped divided into:
Nuclear division Cytoplasmic cleavage
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Types of nuclear division
Mitosis somatic (body) cells Meiosis gametes (sperm
and egg)
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Mitosis
Produces two identical daughter cells Each daughter cell has the same kind and
number of chromosomes as the original parent cell. Used in somatic cells. Whole process is about 24 hours, with 20 of
those being spent in interphase.
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Interphase (Resting stage) Chromosomes cannot be seen because un-wound. Chromosomes duplicate and double in number. Each chromosome now has an identical copy.
These identical copies are called SISTER CHROMATIDS.
Sister chromatids join together at the center point which is called a centromere.
Total number of chromosomes doubles from 46 to 92.
Same in mitosis and meiosis. Not a dividing stage. Rather, a pre-stage to double
up chromosome numbers before division.
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Sister Chromatids vs Homologous Chromosomes
Do not confuse these terms. Homologous chromosomes are
chromosomes which contain the same genes but different alleles. Sister chromatids are identical copies of
each individual chromosome.
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Prophase Chromosomes contract and become darker and
more visible
Each chromosome now consists of two identical sister chromatids
CENTRIOLES move towards the opposite ends (poles) of the cell
MICROTUBULES extend
92 chromosomes total, 46 pairs
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Metaphase
Chromosomes line up at the equator (center of the cell) Spindles are formed to attach to the
centromere of each chromosome 92 chromosomes total, 46 pairs
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Anaphase Sister chromatids separate as individual
chromosomes They move apart towards the opposite poles
92 chromosomes total, 46 pairs.
23 pairs moving to each side.
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Telophase Chromosomes gradually disappear
Nuclear membrane is forming around each
set of chromosomes 23 pairs in each half of the cell in telophase,
46 in each cell. Cytoplasm begins to divide Cytoplasmic
division
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Cytoplasmic division
Division of cytoplasm Separate from nuclear division
Animal cells : by formation of cleavage furrow Plant cells : by formation of cell
plate
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http://www.google.ca/url?sa=i&rct=j&q=cleavage%2Bfurrow&source=images&cd=&cad=rja&docid=8zBReXFIw54RnM&tbnid=PlZTpAvHJ3NARM:&ved=&url=http%3A%2F%2Fhome.apu.edu%2F~jsimons%2FBio101%2Fgenetics.htm&ei=x_HKUfvNHquEiwLFz4CQBQ&bvm=bv.48340889,d.cGE&psig=AFQjCNEVhU2aT7XM7Xsimjo2ZfV4UgxgMQ&ust=1372341063832882http://www.google.ca/url?sa=i&rct=j&q=cell%2Bplate&source=images&cd=&cad=rja&docid=KMjJAeBNoBygmM&tbnid=xza3USZM8ZCmuM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.vcbio.science.ru.nl%2Fen%2Fvirtuallessons%2Fmitostage%2F&ei=JvLKUe_UEcmpiQLCx4CQCQ&bvm=bv.48340889,d.cGE&psig=AFQjCNEbyySHpe86i0bPnA-eLzxi1WeGzw&ust=1372341125372668
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Interphase Animal cell Plant cell
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Prophase Animal cell Plant cell
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Metaphase Animal cell Plant cell
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Anaphase Animal cell Plant cell
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Telophase
Animal cell Plant cell
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Can you identify the different stages of mitosis from the diagram below?
metaphase
anaphase
prophase
interphase
telophase
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Self Learning Exercise
Click the button for a photomicrograph showing the cells of a plant at different stages of mitosis
Q: Arrange the above cells labelled 1 to 4 in the correct sequence of mitosis.
A. 1 --> 2 --> 4 --> 3
B. 3 --> 2 --> 4 --> 1
C. 3 --> 4 --> 2 --> 1
D. 2 --> 3 --> 4 --> 1
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Here is a photomicrograph showing the cells of a plant at different stages of mitosis :
Back
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Sorry, youve got the wrong answer!!!
This is not a correct sequence of mitosis.
Try again...
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Sorry, youve got the wrong answer!!!
This is not a correct sequence of mitosis.
Try again...
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Congratulation!!!
Youve got the correct answer!!!
Click here
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Sorry, youve got the wrong answer!!!
This is not a correct sequence of mitosis.
Try again...
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Self Learning Exercise
Click the button for a photomicrograph showing the cells of a plant at different stages of mitosis Q: What is the DNA content of cell 1 as
compared with that of cell 3?
A. DNA content of cell 1 and cell 3 are the same.
B. DNA content of cell 1 is doubled that in cell 3.
C. DNA content of cell 1 is only half of that in cell 3.
D. DNA content of cell 1 is only quarter of that in cell 3.
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Here is a photomicrograph showing the cells of a plant at different stages of mitosis :
Back
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Sorry, youve got the wrong answer!!!
Remember that chromosomes are made of DNA, and the
chromosomes in cell 3 are duplicated.
Try again...
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Sorry, youve got the wrong answer!!!
Remember that chromosomes are made of DNA, and the
chromosomes in cell 3 are duplicated.
Try again...
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Youve got the correct answer!!!
Go to next question...
Congratulation!!!
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Sorry, youve got the wrong answer!!!
Remember that chromosomes are made of DNA, and the
chromosomes in cell 3 are duplicated.
Try again...
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Self-Learning Exercise
A. 1 and 2 only
B. 1 and 3 only
C. 2 and 3 only
D. 1, 2 and 3
Q: Click this button to see the information for answering this question : Which cells contain the same amount of DNA?
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Information : The photomicrograph below shows some plant cells at different stages of mitosis :
Back to the question
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Sorry, youre wrong!!!
Remember that the different stages of cell division shown is
mitosis!
Try again!!!
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Sorry, youre wrong!!!
Remember that the different stages of cell division shown is
mitosis!
Try again!!!
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Sorry, youre wrong!!!
Remember that the different stages of cell division shown is
mitosis!
Try again!!!
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Congratulations!!!
Click here to end
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Significance of mitosis
To ensure that each daughter cell maintains exactly the same number and kind of chromosomes as the parent cell Mitosis is important in produce more cells for
growth repair replacing dead and damaged cells asexual reproduction
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Meiosis Producing cells with chromosome number
half of the parent cell Cells having pairs of homologous
chromosomes - diploid (2n) e.g. body (somatic) cells
Cells having one chromosome from each homologous pair - haploid (n)
e.g. gametes
Two nuclear divisions Meiosis I and meiosis II
Four haploid cells are produced
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Prophase I
Homologous chromosomes pair up Crossing-over may occur between
homologous chromosomes 92 chromosomes total
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Crossing-over during meiosis
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Metaphase I
Homologous chromosomes line up at the middle of the cell independent assortment 92 chromosomes total
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Independent assortment
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Anaphase I
The 2 members of each homologous pair of chromosomes separate from each other and move to opposite poles of the cell
92 chromosomes total
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Telophase I
Nuclear membrane reforms Followed by cytoplasmic cleavage Each cell has half the chromosome number
as the parent cell 46 in each cell
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Second meiotic division Prophase 2: Same as prophase 1, 2 cells, 46
chromosomes in each cell. No crossing over! Metaphase 2: Same as metaphase 1, 2 cells, 46
chromosomes in each cell. No independent assortment!
Anaphase 2: Same as anaphase 1, 2 cells, 46 chromosomes in each cell. 23 on each side of cell
Telophase 2: Same as telophase 1, 4 cells, 23 chromosomes in each cell. Cells are haploid.
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Prophase 2
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Metaphase 2
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Anaphase 2
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Telophase 2
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Occurrence of meiosis
Plants: anthers and ovules Mammals: testes and ovaries
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What would happen if gametes are formed by mitosis?
Male (2n) Female (2n)
Sperm (2n) Egg (2n)
Zygote (4n)
Sperm/Egg (4n)
Zygote (8n)
Mitosis
Fertilization
Mitosis
Fertilization
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Significance of meiosis
Leads to halving of chromosome number, so to ensure that the diploid number of chromosomes can be restored after fertilization
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Significance of meiosis
Produce genetic variation at crossing-over between homologous
chromosomes during prophase I independent assortment of chromosomes
during metaphase I
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Sources of genetic variation
Crossing-over between homologous chromosomes during meiosis Independent assortment of chromosomes
during meiosis Random fusion of gametes during
fertilization Mutation
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Comparison between mitosis and meiosis
Mitosis Meiosis
Number of division One Two
No. of daughter cell produced by one parent cell
Type of cells produced
Chromosome number of daughter cells
Genetic make-up of daughter cells
Two
Somatic cells
Same as parent cell
Identical to parent cell
Four
Gametes
Half of parent cells
May be different from the parent cell
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Comparison between mitosis and meiosis
Mitosis Meiosis
Pairing of homologous chromosomes
No Yes
Occurrence
Role
Growing tissues
Growth, repair, replacement of old tissues, asexual reproduction
Reproductive tissues
Gamete formation for sexual reproduction
Crossing-over No Yes
Slide Number 1Purposes of Cell DivisionSlide Number 3Slide Number 4What is a chromosome?Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Chromosome NumberSlide Number 13Steps of cell divisionTypes of nuclear divisionMitosisInterphase (Resting stage)Slide Number 18Sister Chromatids vs Homologous ChromosomesProphaseSlide Number 21MetaphaseSlide Number 23AnaphaseSlide Number 25TelophaseSlide Number 27Cytoplasmic divisionSlide Number 29Slide Number 30InterphaseProphaseMetaphaseAnaphaseTelophaseCan you identify the different stages of mitosis from the diagram below?Slide Number 37Here is a photomicrograph showing the cells of a plant at different stages of mitosis :Slide Number 39Slide Number 40Slide Number 41Slide Number 42Slide Number 43Here is a photomicrograph showing the cells of a plant at different stages of mitosis :Slide Number 45Slide Number 46Slide Number 47Slide Number 48Slide Number 49Slide Number 50Slide Number 51Slide Number 52Slide Number 53Slide Number 54Significance of mitosisMeiosisProphase ISlide Number 58Crossing-over during meiosisMetaphase IIndependent assortmentSlide Number 62Anaphase ISlide Number 64Telophase ISlide Number 66Second meiotic divisionProphase 2Metaphase 2 Anaphase 2Telophase 2Occurrence of meiosisWhat would happen if gametes are formed by mitosis?Significance of meiosisSignificance of meiosisSources of genetic variationComparison between mitosis and meiosisComparison between mitosis and meiosis