cell reproduction

Cell Cell ReproductiReproducti

Chromosome Chromosome StructureStructure

• Eukaryotic Eukaryotic cells have cells have their DNA in their DNA in structures structures called called chromosomes.chromosomes.

A cell’s A cell’s chromosomeschromosomes

Modern BiologyModern BiologyPages 144 - 147Pages 144 - 147

• If the nucleus If the nucleus of your cell is of your cell is the size of a the size of a basketball, the basketball, the DNA would be 40 DNA would be 40 miles long!miles long!

E. coli “spills” E. coli “spills” it’s DNAit’s DNA

• Chromosomes:Chromosomes:– Contains a Contains a single DNA single DNA molecule.molecule.

– Have the DNA Have the DNA wrapped wrapped around around proteins proteins called called histones.histones.

Chromosome Chromosome structurestructure

• Chromosomes Chromosomes condense only for condense only for cell cell reproduction.reproduction.

• Condensation:Condensation:– TwistTwist– Become shorterBecome shorter– Become thickerBecome thicker– Become visibleBecome visible

• Chromosomes can Chromosomes can be moved about be moved about cell easier.cell easier.

Chromosome Chromosome condensationcondensation

• Prior to cell Prior to cell reproduction reproduction chromosomes chromosomes replicate.replicate.

• Each copy is Each copy is called a called a chromatid.chromatid.

• Sister chromatids Sister chromatids are connected by are connected by a centromerea centromere

CentromereCentromere

Chromosome Chromosome NumbersNumbers

• Each species Each species has has characteristic characteristic number of number of chromosomes.chromosomes.– Humans = 46Humans = 46– Fruit flies = 8Fruit flies = 8– Crayfish = 200Crayfish = 200– Chimpanzee = 48Chimpanzee = 48

Fruit fly chromosomesFruit fly chromosomes

• Chromosomes are Chromosomes are arranged in arranged in pairs called pairs called homologous homologous pairs.pairs.

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• One pair One pair determines sex: determines sex: sex sex chromosomes.chromosomes.

• All others are All others are called called autosomes.autosomes.

Sex Sex ChromosomesChromosomes

• Either X or Either X or Y. Y. – XX creates XX creates female.female.

– XY creates XY creates male.male.

Sex ChromosomesSex Chromosomes

Haploid Vs Haploid Vs DiploidDiploid

• A karyotype A karyotype shows all shows all homologous pairs homologous pairs matched on a matched on a sheet.sheet.

• Sex chromosomes Sex chromosomes are paired are paired separatelyseparately

Human female Human female karyotyeskaryotyes

• Name two materials that make up Name two materials that make up chromosomes.chromosomes.

• Histones and DNA.Histones and DNA.

• What structure connects chromatids once What structure connects chromatids once the DNA (chromosome) has replicated?the DNA (chromosome) has replicated?

• CentromereCentromere

• What term describes all chromosomes in What term describes all chromosomes in a cell that are identical in males and a cell that are identical in males and females?females?

• AutosomesAutosomes

• What term describes the pair of What term describes the pair of chromosomes that are different in males chromosomes that are different in males and females?and females?

• Sex chromosomesSex chromosomes

• What does the term “haploid” tell you What does the term “haploid” tell you about a cell? Diploid?about a cell? Diploid?

• One of each chromosome pair.One of each chromosome pair.• Homologous pairs of chromosomes.Homologous pairs of chromosomes.

Haploid Vs Haploid Vs DiploidDiploid

• All cells except All cells except gametes have pairs gametes have pairs of chromosomes.of chromosomes.– DiploidDiploid

• Sperm and egg Sperm and egg (gametes) have one (gametes) have one of each pair.of each pair.– haploidhaploid

Human sperm at the Human sperm at the surface of an eggsurface of an egg

Cell DivisionCell Division

• All cells are All cells are derived from derived from division of division of pre-existing pre-existing cells. cells.

• Cell division Cell division is different is different in prokaryotes in prokaryotes and and eukaryotes.eukaryotes.

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Prokaryotic cell Prokaryotic cell reproducingreproducing

Cell Division Cell Division in Prokaryotesin Prokaryotes

• Prokaryotes Prokaryotes reproduce by reproduce by binary fissionbinary fission. .

• Steps in Steps in prokaryote binary prokaryote binary fission.fission.– Chromsome Chromsome

replicatesreplicates– Cell growsCell grows– New cell wall New cell wall

developsdevelops– Cell splits into Cell splits into

two cellstwo cells

Binary FissionBinary Fission

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Cell Division Cell Division in Eukaryotesin Eukaryotes

• Two types of Two types of cell division:cell division:

• Mitosis: Results Mitosis: Results in two daughter in two daughter cells identical to cells identical to the original mother the original mother cell.cell.

• Meiosis: Meiosis: Production of sperm Production of sperm and egg with 1/2 and egg with 1/2 the chromosomes.the chromosomes.

Mitosis in eukaryotic Mitosis in eukaryotic cellscells

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Cell CycleCell Cycle

• G1 Phase G1 Phase – Cell growth, Cell growth, normal normal activityactivity

• S PhaseS Phase– Replication Replication of DNAof DNA

• G2 PhaseG2 Phase– Growth for Growth for cell cell reproduction.reproduction.

• MitosisMitosis• CytokinesisCytokinesis

Eukaryotic cell cycleEukaryotic cell cycle

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InterphaseInterphase

• Consists of Consists of G1, S, G2.G1, S, G2.

• Cell spends Cell spends most time in most time in interphase. interphase.

• Cells may Cells may enter Genter G00 phase.phase.– Do not Do not reproduce.reproduce. InterphaseInterphase

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Stages of Stages of MitosisMitosis

• Preparation Preparation of the of the nucleus for nucleus for binary binary fission.fission.

• Continuous Continuous process divided process divided into four into four stages.stages.

Cells in phases of Cells in phases of mitosismitosis

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• ProphaseProphase– DNA shortens and DNA shortens and thickens.thickens.

– Two centrosomes Two centrosomes appear with two appear with two centrioles.centrioles.

– Nuclear envelope Nuclear envelope breaks down.breaks down.

– Centrioles move Centrioles move to opposite to opposite poles.poles.

– Spindle fibers Spindle fibers are produced.are produced.

Cells in prophaseCells in prophase

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• MetaphaseMetaphase– Chromosmes are Chromosmes are moved to center moved to center of cell.of cell.

– Kinetichore Kinetichore fibers move fibers move chromosomes.chromosomes.

– Fibers are Fibers are connected to connected to kinetichore.kinetichore.

– Polar fibers Polar fibers run from run from centrosome to centrosome to centrosome.centrosome. MetaphaseMetaphase

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• AnaphaseAnaphase– Centromere Centromere splits.splits.

– Chromosomes Chromosomes separate.separate.

– Each copy Each copy moves to moves to opposite opposite pole.pole.

AnaphaseAnaphase

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• TelophaseTelophase– Chromosomes Chromosomes become long become long and slender.and slender.

– New nuclear New nuclear envelope envelope forms.forms.

– Nucleolus Nucleolus forms.forms.

– Spindle Spindle fibers fibers breakdown.breakdown.

TelophaseTelophase

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Plant Vs Animal Plant Vs Animal MitosisMitosis

Animal Animal InterphaseInterphase

Plant Plant InterphaseInterphase

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Animal Animal ProphaseProphase

Plant Plant ProphaseProphase

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Animal Animal MetaphaseMetaphase

Plant Plant MetaphaseMetaphase

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Animal Animal AnaphaseAnaphase

Plant AnaphasePlant Anaphase

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Animal Animal TelophaseTelophase

Plant Plant TelophaseTelophase

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MeiosiMeiosiss

MeiosisMeiosis• Meiosis is a process by which the Meiosis is a process by which the chromosome number is reduced by half.chromosome number is reduced by half.

–Only occurs in testes and Only occurs in testes and ovaries.ovaries.–Only occurs in cells called Only occurs in cells called “germ” cells.“germ” cells.–Used to produce sperm and eggs.Used to produce sperm and eggs.

Meiosis (cont)• Chromosomes Chromosomes

in all cells in all cells of all of all organisms organisms are in pairs are in pairs referred to referred to as as homologous homologous pairs.pairs.

• These pairs These pairs must be must be split during split during the process the process of meiosisof meiosis

• Cells undergo the Cells undergo the phases G1, S, & G2 phases G1, S, & G2 prior to meiosis.prior to meiosis.

• Cells that undergo Cells that undergo meiosis start as meiosis start as diploid (2n) diploid (2n) cells.cells.

• Meiosis results in Meiosis results in four haploid (1n) four haploid (1n) cells being cells being produced.produced.

Prior to the Process Meiosis

• Meiosis is known Meiosis is known as “reduction as “reduction and division”and division”

• Chromosomes # is Chromosomes # is reduced from 2n reduced from 2n to 1n.to 1n.

• Divisions of the Divisions of the cell result in 4 cell result in 4 cells being cells being produced.produced.

• A diploid cell A diploid cell (2n) has a pair (2n) has a pair of each of each chromosome.chromosome.

• These pairs are These pairs are referred to as referred to as homologous.homologous.

• One “homologue” One “homologue” of a pair came of a pair came from mom and from mom and the other from the other from dad.dad.

• After After meiosis is meiosis is complete complete only one of only one of each type each type of of chromosome chromosome is present is present in a sperm in a sperm or egg.or egg.

Meiosis IMeiosis I• Prophase IProphase I

– Homologous Homologous pairs align pairs align with each with each other.other.

– Synapsis Synapsis occurs.occurs.

– Synaptonemal Synaptonemal complex holds complex holds homologues in homologues in place.place.

– Crossing over Crossing over occurs. (At occurs. (At chiasma)chiasma)

Meiosis IMeiosis I• Metaphase IMetaphase I

– MicrotubuleMicrotubules attach s attach only to only to outside outside kinetochorekinetochores.s.

– Homologous Homologous pairs move pairs move to equator to equator of cell due of cell due to to kinetochore kinetochore fibers.fibers.

Meiosis IMeiosis I• Anaphase IAnaphase I

– Homologues Homologues are pulled are pulled apart by apart by kinetochore kinetochore fibers.fibers.

– Homologous Homologous pairs are pairs are separated and separated and moved to moved to opposite opposite poles.poles.

Meiosis IMeiosis I• Telophase Telophase II– Cell goes Cell goes through through cytokinescytokinesis.is.

– Cells are Cells are now 1n or now 1n or haploid.haploid.

Meiosis IIMeiosis II• Prophase Prophase IIII– No No replicatreplicationion

– No No synapsissynapsis

– No No crossing crossing over.over.

Meiosis IIMeiosis II

Centromeres Centromeres eventually eventually

split.split.

Chromosomes Chromosomes are moved to are moved to poles of poles of cell.cell.A second A second division division occurs.occurs.

• Crossing over Crossing over occurs during occurs during tetrad tetrad positioning of positioning of chromosomes.chromosomes.

• Results in Results in genetic genetic recombinationrecombination

Crossing Crossing OverOver

• Actual picture of chromosomes crossing over.Actual picture of chromosomes crossing over.• This creates variation among offspring of a species.This creates variation among offspring of a species.

Crossing Crossing OverOver

Contrasting Mitosis & Contrasting Mitosis & MeiosisMeiosis

• MitosisMitosis– Occurs each time a Occurs each time a “body cell” “body cell” replicatesreplicates

– Homologues are Homologues are randomly randomly distributed across distributed across metaphase platemetaphase plate

– Crossing over Crossing over never occurs.never occurs.

– Sister chromatids Sister chromatids remain identical.remain identical.

– Sister chromatids Sister chromatids separate in separate in anaphase I.anaphase I.

• MeiosisMeiosis– Occurs only in Occurs only in germ cells of germ cells of ovaries and ovaries and testes.testes.

– Homologous pairs Homologous pairs align (synapsis)align (synapsis)

– Crossing over Crossing over occurs.occurs.

– Sister chromatids Sister chromatids are genetically are genetically differentdifferent

– Sister chromatids Sister chromatids do not separate in do not separate in anaphase Ianaphase I

Comparing Mitosis and Meiosis

EmbryologyEmbryology• SpermatogenesisSpermatogenesis results in 4 results in 4 mature sperm mature sperm from each germ from each germ cell.cell.

• Meiosis Meiosis reduced reduced the chromosome the chromosome number from number from pairs (diploid) pairs (diploid) to 1 of each to 1 of each homologous pair homologous pair (1n).(1n).

There are 23 chromosomes There are 23 chromosomes in the human sperm. It in the human sperm. It will contain 22 autosomes will contain 22 autosomes and either an “X” or a and either an “X” or a “Y” sex chromosome“Y” sex chromosome

• Oogenesis Oogenesis creates creates haploid eggs.haploid eggs.

• The egg The egg contains 22 contains 22 autosomes and autosomes and an “X” sex an “X” sex chromosome. chromosome.

• The egg also The egg also contains a contains a polar body.polar body.

The egg and the polar body. The egg and the polar body. The polar body will be expelled The polar body will be expelled if fertilization occursif fertilization occurs

Modern BiologyModern BiologyPages 682 - 684Pages 682 - 684EmbryologyEmbryology

EmbryologEmbryologyy

• 1n egg is 1n egg is fertilized by fertilized by 1n sperm.1n sperm.

• 2n zygote is 2n zygote is formed.formed.

• The zygote is a The zygote is a single cell.single cell.

• The zygote then The zygote then goes through goes through mitosis and mitosis and cytokinesis.cytokinesis. A fertilized egg A fertilized egg

with two nuclei with two nuclei about to fuseabout to fuse

EmbryologyEmbryology• Each set of Each set of cell divisions cell divisions are referred are referred to as to as cleavage.cleavage.

• Each set of Each set of divisions divisions reduces the reduces the cell size.cell size.

• Cleavage Cleavage increases the increases the surface area surface area to volume to volume ratio.ratio.

The zygote has just The zygote has just cleaved to form a 2 cell cleaved to form a 2 cell

morula.morula.

EmbryologyEmbryology

• Successive Successive cleavages cleavages create 4,8, create 4,8, 16, 32, and 64 16, 32, and 64 cell embryos.cell embryos.

• Embryo called Embryo called a a morulamorula at at this stage.this stage.

• Embryo remains Embryo remains same size.same size.

Another cleavage Another cleavage results in 4 cell results in 4 cell

morula.morula.

• The embryo then The embryo then takes on the shape takes on the shape of a hollow ball.of a hollow ball.

• Blastula is Blastula is composed of a composed of a single cell layer.single cell layer.– EctodermEctoderm

• Embryo is still Embryo is still the same size as the same size as the fertilized the fertilized egg.egg.

BlastulaBlastula

EmbryologyEmbryology

• The blastula The blastula then folds then folds inward to form inward to form a gastrula.a gastrula.

• This process This process is is gastrulation.gastrulation.

• The embryo now The embryo now has 2 cell has 2 cell layers.layers.– Inner Inner “endoderm”“endoderm”

– Outer Outer “ectoderm”“ectoderm”

An embryo going through An embryo going through gastrulation. The most gastrulation. The most

dangerous time of our lives.dangerous time of our lives.

• A third cell A third cell layer develops layer develops between the between the ectoderm and ectoderm and endoderm.endoderm.– Mesoderm.Mesoderm.

• Germ layers Germ layers develop into develop into different organ different organ systems.systems.

A fully formed gastrula with A fully formed gastrula with an ectoderm and an endoderman ectoderm and an endoderm

Human fetus just a few weeks Human fetus just a few weeks old and just a couple of old and just a couple of

inches in lengthinches in length

• EctodermEctoderm– Skin and nervous Skin and nervous system.system.

• EndodermEndoderm– Lining of Lining of digestive system.digestive system.

• MesodermMesoderm– Everything in Everything in between.between.

– MusclesMuscles– BonesBones– Circulatory Circulatory systemsystem

• Using your notes and directed Using your notes and directed reading 8.1 complete the following reading 8.1 complete the following quick write;quick write;

• Explain the structure of a Explain the structure of a chromosome such as those found in chromosome such as those found in the human cell. the human cell.

• Contrast sex chromosomes and Contrast sex chromosomes and autosomes. autosomes.

• Contrast a haploid cell and Contrast a haploid cell and diploid cell in terms of diploid cell in terms of chromosomes. Give examples of chromosomes. Give examples of each type. each type.

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