Cell DivisionCell Division

How to make moreHow to make more

What we are going to investigate.What we are going to investigate.

A review of the A review of the structure of the structure of the chromosomechromosome

Why cells divideWhy cells divideMitosisMitosisMeiosisMeiosisCancer cellsCancer cells

Genetic Variation Genetic Variation associated with cell associated with cell divisiondivision

Diseases of non-Diseases of non-disjunctiondisjunction

Why do we need to learn this?Why do we need to learn this?So that we can understand how our bodies So that we can understand how our bodies

work.work.So we can have a deeper understanding So we can have a deeper understanding

of how reproduction really works and what of how reproduction really works and what can go wrong.can go wrong.

To understand how some genetic To understand how some genetic disorders arise.disorders arise.

So that when you or any of the So that when you or any of the multicellular organisms around you have multicellular organisms around you have offspring, you understand where their offspring, you understand where their genetic material comes from.genetic material comes from.

ReviewReviewWhat are the parts of a What are the parts of a

chromosome?chromosome?

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GenesGenesA A GeneGene is a sequence of DNA that is a sequence of DNA that

instructs a cell to produce proteinsinstructs a cell to produce proteins It is the unit of inheritanceIt is the unit of inheritance

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DNADNADNA DNA

(Deoxyribonucleic (Deoxyribonucleic Acid) Acid)

is the chemical is the chemical whose building block whose building block sequence encodes sequence encodes the information that a the information that a cell uses to construct cell uses to construct a particular protein.a particular protein.

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Structure of a ChromosomeStructure of a ChromosomeA A ChromosomeChromosome is a highly coiled is a highly coiled

and condensed strand of DNA and condensed strand of DNA wrapped around proteins called wrapped around proteins called histones.histones.

A A ChromosomeChromosome is made from a is made from a single strand of DNA and contains single strand of DNA and contains many genesmany genes..

Structure of a ChromosomeStructure of a Chromosome

A A ChromatidChromatid – A single, very condensed – A single, very condensed strand of DNA. Half of a chromosome.strand of DNA. Half of a chromosome.

A A CentromereCentromere – The largest constriction – The largest constriction in a chromosome. This is the place where in a chromosome. This is the place where the chromatids are held together.the chromatids are held together.

A A KinetichoreKinetichore – The area of the – The area of the chromosome where the spindle fibers chromosome where the spindle fibers attach.attach.

A A TelomereTelomere – A chromosome tip. – A chromosome tip.

Chromosome PartsChromosome Parts

Kinetichore

Telomere

Why do we need to make more Why do we need to make more cells?cells?

1.1. GrowthGrowth

2.2. RepairRepair

3.3. ReproductionReproduction

What would happen if we could not make What would happen if we could not make new cells?new cells?

What happens when our cells will What happens when our cells will not stop multiplying?not stop multiplying?

CancerCancer Understanding diseases typically requires Understanding diseases typically requires

scientists to examine basic cellular processesscientists to examine basic cellular processes Uncontrolled cell division is a form of cancerUncontrolled cell division is a form of cancer Understanding those processes can help health Understanding those processes can help health

care workers develop better prevention and care workers develop better prevention and treatment strategies. treatment strategies.

You have to know how something works in order You have to know how something works in order to fix it!to fix it!

The Cell CycleThe Cell CycleRegular sequence of growth and division.Regular sequence of growth and division.

Cell cycle rates varyCell cycle rates varyA brain cell may never divideA brain cell may never divideEmbryos divide rapidlyEmbryos divide rapidly

This is a continuous process that we This is a continuous process that we study in stepsstudy in steps

InterphaseInterphase Interphase Interphase is the major stage of cell division where is the major stage of cell division where

the cell is not dividing, but there is a lot of cell activity.the cell is not dividing, but there is a lot of cell activity.

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Interphase is divided into 3 phasesInterphase is divided into 3 phases

G1 (Gap phase 1) G1 (Gap phase 1) Cell is making protein, carbohydrates, and lipids.Cell is making protein, carbohydrates, and lipids. Time in G1 varies greatly.Time in G1 varies greatly.

S (Synthesis phase)S (Synthesis phase) Cell replicates it’s genome (DNA)Cell replicates it’s genome (DNA) Proteins that make the spindle fibers are produced.Proteins that make the spindle fibers are produced. Microtubules form centrioles near the nucleus in animal Microtubules form centrioles near the nucleus in animal

cells.cells.

G2 (Gap phase 2)G2 (Gap phase 2) Cell makes more proteins for membranes of daughter cellsCell makes more proteins for membranes of daughter cells

Two Types of Cell DivisionTwo Types of Cell DivisionMitosisMitosis The division of two The division of two

somatic (non-sex) cellssomatic (non-sex) cells Produces two identical Produces two identical

daughter cells.daughter cells. Daughter cells have the Daughter cells have the

same number of same number of chromosomes as the chromosomes as the parent cell parent cell

Diploid chromosome # is Diploid chromosome # is the total chromosome # the total chromosome # for a species for a species

MeiosisMeiosis A type of cell division A type of cell division

that halves the usual that halves the usual number of chromosomes number of chromosomes to form haploid gametesto form haploid gametes

A A gamete gamete is a sex cell is a sex cell (Sperm or Egg)(Sperm or Egg)

Cells have half the Cells have half the chromosome number of chromosome number of the parent cell (the parent cell (haploidhaploid))

Stages of Mitosis: ProphaseStages of Mitosis: Prophase Microtubules Microtubules

assemble to form assemble to form spindlespindle

Nuclear membrane Nuclear membrane breaks downbreaks down

Nucleus no longer Nucleus no longer visiblevisible

DNA is condensed DNA is condensed

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MetaphaseMetaphase Chromosomes Chromosomes

attach to spindle at attach to spindle at their centromeres.their centromeres.

They line up at the They line up at the center of the cell.center of the cell.

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AnaphaseAnaphase Cell membrane indents Cell membrane indents

at middleat middle Centromeres part and Centromeres part and

chromatids move to chromatids move to opposite ends of the opposite ends of the cellcell

When the split occurs, When the split occurs, each daughter cell each daughter cell receives one chromatid receives one chromatid from each replicated from each replicated chromosomechromosome

Cell stretchesCell stretches

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TelophaseTelophase Spindle falls apartSpindle falls apart Nuclear membranes Nuclear membranes

formform Chromosomes thin outChromosomes thin out CytokinesisCytokinesis – –

organelles distributed organelles distributed between two daughter between two daughter cellscells

Cells separateCells separate Diploid cellsDiploid cells - the two - the two

daughter cells have the daughter cells have the same number of same number of chromosomes as the chromosomes as the original parent celloriginal parent cell

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Cytokinesis in Plant CellsCytokinesis in Plant Cells

Cytokinesis in Animal CellsCytokinesis in Animal Cells

Mitosis

MeiosisMeiosisProduces sex cells: Sperm and Oocyte Produces sex cells: Sperm and Oocyte

(Egg) cells(Egg) cellsHaploid cellsHaploid cells -the final daughter cells -the final daughter cells

have half the chromosomal number of the have half the chromosomal number of the original parent cell. original parent cell.

Example: Human somatic cells have 46 Example: Human somatic cells have 46 chromosomes.chromosomes.

Human sex cells have 23 chromosomes.Human sex cells have 23 chromosomes.Why do the sex cells only need half of the Why do the sex cells only need half of the

chromosomes?chromosomes?

Homologous PairsHomologous PairsChromosome pairs (one from mom and Chromosome pairs (one from mom and

one from dad) that have the same genes one from dad) that have the same genes in the same order but may have different in the same order but may have different alleles, or forms of the same gene.alleles, or forms of the same gene.

Meiosis: TWO DivisionsMeiosis: TWO Divisions 11stst Division = Meiosis 1 Division = Meiosis 1 The number of The number of

chromosomes replicates chromosomes replicates from 46 in humans to 92. from 46 in humans to 92. When cell divides, each When cell divides, each daughter cell has 46 daughter cell has 46 chromosomes.chromosomes.

22ndnd Division = Meiosis 2 Division = Meiosis 2 Produces four cells from the Produces four cells from the

two cells formed in meiosis two cells formed in meiosis 1.1.

Daughter cells from meiosis Daughter cells from meiosis 1 have 46 chromosomes. 1 have 46 chromosomes. When they divide they form 4 When they divide they form 4 cells that each have 23 cells that each have 23 chromosomes.chromosomes.

Important to note that Important to note that chromosomes do not chromosomes do not replicate in the 2replicate in the 2ndnd division division..

Meiosis

SpermatogenesisSpermatogenesis The formation of sperm The formation of sperm

cells.cells. SpermatogoniumSpermatogonium – –

diploid cell that divides diploid cell that divides through mitosis making 2 through mitosis making 2 daughter cells. One daughter cells. One continues to divide continues to divide mitotically while the mitotically while the other becomes other becomes specialized. specialized.

That cell is the That cell is the Primary Primary Spermatocyte.Spermatocyte.

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SpermatogenesisSpermatogenesis Primary SpermatocytePrimary Spermatocytes s

(A diploid cell) undergo (A diploid cell) undergo meiosis 1meiosis 1

They make They make Secondary Secondary SpermatocytesSpermatocytes (haploid (haploid cells)cells)

In meiosis 2 In meiosis 2 Secondary Secondary SpermatocytesSpermatocytes divide divide to make Sto make Spermatids.permatids.

The SThe Spermatid permatid specializes and develops specializes and develops a tail (flagellum)a tail (flagellum)

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OogenesisOogenesisMeiosis in the femaleMeiosis in the femaleOogoniumOogonium – diploid cell that divides during – diploid cell that divides during

meiosis 1.meiosis 1.Primary OocytePrimary Oocyte – an – an OogoniumOogonium that has that has

grown, accumulated cytoplasm, and replicated grown, accumulated cytoplasm, and replicated its DNA.its DNA.

Primary OocytePrimary Oocyte divides into two cells: divides into two cells: WARNING DIFFERENCE HERE!!WARNING DIFFERENCE HERE!!

A A Polar BodyPolar Body – a small cell with very little – a small cell with very little cytoplasmcytoplasm

A A Secondary OocyteSecondary Oocyte – A much larger cell. – A much larger cell. Both cells are haploidBoth cells are haploid

OogenesisOogenesis In meiosis 2 the In meiosis 2 the Polar BodyPolar Body divides into two divides into two

small polar bodies and they are reabsorbed.small polar bodies and they are reabsorbed.

What A Waste!What A Waste!• The Secondary Oocyte divides to produce The Secondary Oocyte divides to produce

another polar body and a mature egg cell or another polar body and a mature egg cell or Ovum.Ovum.

• The Ovum has a large amount of cytoplasm.The Ovum has a large amount of cytoplasm.

Comparison of Mitosis to MeiosisComparison of Mitosis to MeiosisMitosisMitosis

1.1. One DivisionOne Division2.2. Two Daughter Cells Per Two Daughter Cells Per

CycleCycle3.3. Daughter Cells Daughter Cells

Genetically IdenticalGenetically Identical4.4. Chromosomal Number Chromosomal Number

of Daughter Cells the of Daughter Cells the Same as the Parent Same as the Parent Cell (2n)Cell (2n)

5.5. Occurs in Somatic CellsOccurs in Somatic Cells6.6. Used for Growth, Used for Growth,

Repair, and Sexual Repair, and Sexual ReproductionReproduction

MeiosisMeiosis1.1. Two DivisionsTwo Divisions2.2. Four Daughter Cells Four Daughter Cells

Per CyclePer Cycle3.3. Daughter Cells Daughter Cells

Genetically DifferentGenetically Different4.4. Chromosomal Number Chromosomal Number

of Daughter Cells Half of Daughter Cells Half that of Parent Cell (1n)that of Parent Cell (1n)

5.5. Occurs in Gamete Occurs in Gamete ProductionProduction

6.6. Used for Sexual Used for Sexual Reproduction and Reproduction and Genetic VariationGenetic Variation

Genetic VariationGenetic Variation

Independent Assortment of ChromosomesIndependent Assortment of ChromosomesCrossing-overCrossing-overRandom Fertilization of an Ovum by a Random Fertilization of an Ovum by a

SpermSpermNondisjunctionNondisjunction

Independent Assortment of Independent Assortment of ChromosomesChromosomes

Homologous pairs line up randomly during Homologous pairs line up randomly during metaphase 1.metaphase 1.

50% chance of getting either option. 50% chance of getting either option.

Crossing-overCrossing-over

Produces Produces Recombinant Recombinant ChromosomesChromosomes

NondisjunctionNondisjunction