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Cellular Division

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Cell DivisionAll cells are derived from

pre-existing cellsNew cells are produced for

growth and to replace damaged or old cells

Differs in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, & animals)

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Prokaryotic ChromosomeThe DNA of

prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane

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Eukaryotic ChromosomesAll eukaryotic cells store

genetic information in chromosomes

Most eukaryotes have between 10 and 50 chromosomes in their body cells

Human body cells have 46 chromosomes or 23 identical pairs

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Chromosomes in Dividing Cells

Duplicated chromosomes are called chromatids & are held together by the centromere

Called Sister Chromatids

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KaryotypeA picture of the

chromosomes from a human cell arranged in pairs by size

First 22 pairs are called autosomes

Last pair are the sex chromosomes

XX female or XY male

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Boy or Girl?

Y - Chromosome

X - Chromosome

The Y Chromosome Decides

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Cell Reproduction

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Types of Cell ReproductionAsexual reproduction involves

a single cell dividing to make 2 new, identical daughter cells

Mitosis, binary fission, and budding are examples of asexual reproduction

Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cells

Meiosis is an example

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Cell Division in Prokaryotes

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Identical Daughter Cells

Parent Cell

Two identical daughter

cells

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Cell Division in ProkaryotesProkaryotes such

as bacteria divide into 2 identical cells by the process of binary fission

Single chromosome makes a copy of itself

Cell wall forms between the chromosomes dividing the cell

Parent cell

2 identical daughter cells

Chromosome

replicates

Cell splits

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Prokaryotic Cell Undergoing Binary

Fission

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The Cell Cycle

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Five Phases of the Cell Cycle

G1 - primary growth phaseS – synthesis; DNA

replicatedG2 - secondary growth

phasecollectively these 3 stages are called interphase

M – mitosis (4 phases)C - cytokinesis

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Cell Cycle

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Interphase - G1 Stage

1st growth stage after cell division

Cells mature by making more cytoplasm & organelles

Cell carries on its normal metabolic activities

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Interphase – S StageSynthesis stageDNA is copied or replicated

Two identic

al copies of DNA

Original DNA

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Interphase – G2 Stage2nd Growth StageOccurs after DNA has been

copiedAll cell structures needed for

division are made (e.g. centrioles)

Both organelles & proteins are synthesized

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Sketch the Cell Cycle

Daughter Cells

DNA Copied

Cells Matur

e

Cells prepare for Division

Cell Divides into Identical cells

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Mitosis

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MitosisDivision of the

nucleusOnly occurs in

eukaryotesHas four

stagesDoesn’t occur

in some cells such as brain cells

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Four Mitotic Stages

ProphaseMetaphaseAnaphaseTelophase

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CytokinesisMeans division of the cytoplasm

Division of cell into two, identical halves called daughter cells

In plant cells, cell plate forms at the equator to divide cell

In animal cells, cleavage furrow forms to split cell

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CytokinesisCleavage furrow in

animal cell

Cell plate in plant cell

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Mitotic Stages

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Daughter Cells of MitosisHave the same number of

chromosomes as each other and as the parent cell from which they were formed

Identical to each other, but smaller than parent cell

Must grow in size to become mature cells (G1 of Interphase)

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Interphase

Prophase

MetaphaseAnaphase

Telophase

Name the Stages:

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Eukaryotic Cell Division Used for growth and

repair Produce two new

cells identical to the original cell

Cells are diploid (2n)Chromosomes

during Metaphase of mitosis

Prophase

Metaphase AnaphaseTelophaseCytokinesis

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Mitosis AnimationName each stage as you see it

occur?

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Mitosis in Onion Root Tips

Do you see any stages of mitosis?

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Uncontrolled Mitosis If mitosis is not

controlled, unlimited cell division occurs causing cancerous tumors

Oncogenes are special proteins that increase the chance that a normal cell develops into a tumor cell

Cancer cells

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MeiosisFormation of

Gametes (Eggs & Sperm)

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Facts About MeiosisDaughter cells contain half the

number of chromosomes as the original cell

Produces gametes (eggs & sperm)

Occurs in the testes in males (Spermatogenesis)

Occurs in the ovaries in females (Oogenesis)

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Start with 46 double stranded chromosomes (2n)

After 1 division - 23 double stranded chromosomes (n)

After 2nd division - 23 single stranded chromosomes (n)

  Occurs in our germ cells that produce gametes

More Meiosis Facts

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Why Do we Need Meiosis?

It is the fundamental basis of sexual reproduction

Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote

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Meiosis Forms Haploid Gametes

Meiosis must reduce the chromosome number by half

Fertilization then restores the 2n number

from mom from dad child

meiosis reducesgenetic content

toomuch!

The right number!

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Crossing-OverHomologous

chromosomes in a tetrad cross over each other

Pieces of chromosomes or genes are exchanged

Produces Genetic recombination in the offspring

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Crossing-over multiplies the already huge number of different gamete types produced by independent

assortment

Crossing-Over

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GametogenesisOogenesis

or Spermatogenesis

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SpermatogenesisOccurs in the

testesTwo divisions

produce 4 spermatids

Spermatids mature into sperm

Men produce about 250,000,000 sperm per day

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Spermatogenesis in the Testes

Spermatid

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OogenesisOccurs in the ovariesTwo divisions produce 3 polar

bodies that die and 1 eggPolar bodies die because of

unequal division of cytoplasmImmature egg called oocyteStarting at puberty, one oocyte

matures into an ovum (egg) every 28 days

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Oogenesis in the Ovaries

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Oogenesis

Oogonium(diploid)

Mitosis

Primaryoocyte(diploid)

Meiosis I

Secondaryoocyte(haploid)

Meiosis II(if fertilizationoccurs)

First polar bodymay divide (haploid) Polar

bodiesdie

Ovum (egg)

Secondpolar body(haploid)

a

A

X

X

a

X

A X

a

X

a

X

Matureegg

A

X

A

X

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Comparing Mitosis and

Meiosis

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Mitosis MeiosisNumber of

divisions 1 2

Number of daughter cells 2 4

Genetically identical? Yes No

Chromosome # Same as parent Half of parent

Where Somatic cells Germ cells

When Throughout life

At sexual maturity

Role Growth and repair

Sexual reproduction

Comparison of Divisions