cell division
TRANSCRIPT
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Cell Division
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DNADNA – large molecule that stores
hereditary (genetic) information.- found in the nucleus of a cell.
- controls cell division.
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ChromosomesChromosomes – MANY strands of
DNA wound together into threadlike structures.
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Cell DivisionCell Division – a cell that is dividing into
two new cells.
- the two new cells are daughter cells.
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MitosisMitosis – two daughter cells with exact
same genetic material (DNA) are produced.
- daughter cells have same number of chromosomes as parent cell.
6 chromosomes 6 chromosomes
6 chromosomes
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InterphaseInterphase – preparation stage BEFORE
Mitosis where the cell grows and duplicates materials.
- Longest stage of Cell Cycle
- Copies chromosomes!
- Organelles double.
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ProphaseProphase – first phase of Mitosis where
DNA winds into chromosomes.
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Prophase
Chromosomes
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Metaphase
Metaphase – chromosomes line up along the middle of the cell.
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Metaphase
Chromosomes
Middle (equator) of cell
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Anaphase
Anaphase – chromosomes are “pulled” apart!
- move to opposite sides of cell.
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Anaphase
Single Chromosome
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Telophase
Telophase – “ending” phase of Mitosis.
- two new cells form.
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Telophase
New nuclei
Chromosomes unwinding
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End Results of Mitosis
4 chromosomes at start
Chromosomes double into 2 strands (8)
4 chromosomes in each new cell at end
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What kinds of cells do Mitosis?Single-celled organisms - mitosis as a
form of asexual reproduction.
Multicellular organisms - mitosis in repair and replacement of body cells (hair, skin, etc.)
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Cancer: Uncontrolled DivisionNormal cells will stop dividing when they
come in contact with other cells.
Cancer – disease where cells do not stop dividing and ignore signals from other cells.
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What is the Purpose of Reproduction?
To form new individuals (offspring) of a species.
2 Types:
1. Asexual Reproduction – reproduction involving only one parent.
2. Sexual Reproduction – reproduction involving two parents.
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Asexual Reproduction
Offspring are identical and contain same amount of genetic material as parents.
- Results from mitosis.
Ex: a. Budding
b. Binary Fission
c. Vegetative Propogation
d. Sporulation
e. Regeneration
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Sexual Cell Division: Meiosis
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Chromosome NumberHuman body cell – 46 chromosomes
Arranged in 23 pairs (23 X 2=46).
Homologous Chromosomes – a pair of chromosomes with
same size, shape, etc.
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DiploidDiploid – body cells that contain two sets
of chromosomes.
- Ex: skin, hair, heart, liver, muscle cells, etc.
- Written as 2n.
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HaploidHaploid – gamete (sex) cells which
contain only one set of chromosomes.
- Ex: sperm/egg cells.
- Written as n.
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MeiosisMeiosis – type of cell division used to
produce gametes (sex cells).
Two functions:1. Forms cells with half the number of
chromosomes. (23 chromosomes in both egg and sperm)
2. Rearrange chromosomes for genetic differences from parents (variability).
3. Two sets of phases whereas Mitosis only has one set.
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Meiosis Overview
4 Chromosomes
2 Chromosomes in each cell
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Meiosis in MalesMeiosis in males produces four sperm
(n) cells which are all functional.
2n
n
n
n
n
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Meiosis in FemalesMeiosis in females produces four egg (n)
cells. Only one is functional!
2n
n
n
n
n
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Meiosis = Genetic VariationMeiosis is responsible for genetic
differences in new cells:
1. Chromosomes lineup in different ways.
2. Crossing over – swapping pieces of chromosomes.
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Mitosis Vs. Meiosis
Mitosis Meiosis
# of parent cells 1 2
# of cells produced 2 4
Appearance of Identical Different
offspring
Types of cells Body Gametes
(egg/sperm)
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Meiosis I
Interphase I – DNA is unwound as chromatin.
- DNA duplicates.
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Prophase I –chromosomes become visible and double-stranded.
- Homologous chromosomes pair up.
- Crossing over – pieces of chromosomes are swapped.
Homologous chromosomes
Homologous chromosomes
Meiosis I
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Metaphase I –pairs of homologous chromosomes lineup in the middle of the cell.
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Anaphase I – homologous chromosomes separate (not into single-stranded chromosomes or chromatids).
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Telophase I – two haploid daughter cells are formed.
- nuclear membrane
returns!
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Meiosis II (like Mitosis)
Prophase II – two haploid daughter cells now enter meiosis II.
- cell has completely divided and chromosomes are separated.
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Metaphase II – chromosomes (non-homologous) line up in the middle of each cell.
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Anaphase II – double-stranded chromosomes split into single-stranded chromosomes (chromatids).
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Telophase II – four haploid cells are formed each with single-stranded chromosomes (chromatids).