Cell ReproductionCell Reproductionand Divisionand Division

Ch 8Ch 8

ChromosomesChromosomes• ChromosomeChromosome: DNA wrapped up: DNA wrapped up

w/ w/ histoneshistones (proteins) = organized (proteins) = organized

• ChromatinChromatin: uncoiled : uncoiled chromosome= unorganized DNAchromosome= unorganized DNA

Chromosome #Chromosome #

•All species All species have their own have their own characteristic # characteristic # of of chromosomes chromosomes in each cellin each cell

Chromosome NumberChromosome Number

• Diploid Diploid 2n2n: : pairs of pairs of chromosomes (1 from each chromosomes (1 from each parentparent

• Haploid Haploid 1n1n: : unpaired unpaired chromosomes (sperm or chromosomes (sperm or egg)egg)

Chromosome TerminologyChromosome Terminology

1 Chromosome With 2 chromatids(duplicated)

1 Chromosome

2 chromosomes (Unduplicated)

2 chromosomes(both duplicated)If these are homologous it is a tetrad

Centromere

Centromere

Chromosome TypesChromosome TypesSEX CHROMOSOMESSEX CHROMOSOMES

Determine GenderDetermine Gender–Males: XYMales: XY–Females: XXFemales: XX–Male determines gender of the Male determines gender of the

babybabyAUTOSOMESAUTOSOMES• All non-sex chromosomesAll non-sex chromosomes

How many C’somes do you How many C’somes do you have?have?

• Humans: 23 pair Humans: 23 pair = 46 = 46 chromosomeschromosomes• Karyotype: Karyotype:

arrangement of arrangement of an individuals an individuals chromosomes chromosomes

Homologous ChromosomesHomologous Chromosomes• Have the same Have the same

type of information type of information but with different but with different detailsdetails• #2 from mom has #2 from mom has

same kind of info same kind of info as #2 from dad as #2 from dad

•Which ones aren’t homologous?Which ones aren’t homologous?

Haploid/DiploidHaploid/Diploid

2525

Cell DivisionCell Division

Cell Division in ProkaryotesCell Division in Prokaryotes

• Binary Fission-Bacterial Cells Binary Fission-Bacterial Cells reproduce asexuallyreproduce asexually

Mitosis & Cell Division In EukaryotesMitosis & Cell Division In Eukaryotes

• When a cell gets too big, it divides When a cell gets too big, it divides or stops growingor stops growing

• Eukaryotes first divide nucleus =Eukaryotes first divide nucleus = MitosisMitosis, , then divide the rest =then divide the rest = cytokinesiscytokinesis

Cell CycleCell Cycle• A cells life is A cells life is

divided into a divided into a cyclecycle• Interphase, Interphase,

Mitosis & Mitosis & Cytokinesis are Cytokinesis are steps in the steps in the cyclecycle

Stages of the cell cycleStages of the cell cycle• INTERPHASE = most active & majority of timeINTERPHASE = most active & majority of time– G1G1 stage = "GAP 1” - intense growth stage = "GAP 1” - intense growth– SS stage = "Synthesis” stage = "Synthesis” • DNA replication occurs-IT DOUBLES!DNA replication occurs-IT DOUBLES!

– G2 G2 stage = "GAP 2” - duplicate organellesstage = "GAP 2” - duplicate organelles– G0G0 stage = exit cycle & never divide again stage = exit cycle & never divide again

(CNS=nerve cells)(CNS=nerve cells)• MITOSISMITOSIS– M M stage = mitosis - nucleus dividesstage = mitosis - nucleus divides

• Divided into Divided into PMATPMAT

• Cytokinesis Cytokinesis = cell divides= cell divides

InterphaseInterphase• The cell is metabolizing, growing and The cell is metabolizing, growing and

preparing for mitosispreparing for mitosis

• Chromosomes are Chromosomes are notnot clearly seen clearly seen

• Where a cell spends most of its lifeWhere a cell spends most of its life

Controlling the Cell CycleControlling the Cell Cycle• Length variesLength varies• 3 checkpoints based on proteins3 checkpoints based on proteins–G1, G2 and MitosisG1, G2 and Mitosis

• Errors can lead to cancer.Errors can lead to cancer.– In cancer, regulation of the cell cycle In cancer, regulation of the cell cycle

is lostis lost–Normal cell growth & behavior is lost. Normal cell growth & behavior is lost.

What is Mitosis?What is Mitosis?• Nuclear divisionNuclear division

• Produces Produces two identical daughter two identical daughter cellscells during prophase, metaphase, during prophase, metaphase, anaphase, and telophase (PMAT). anaphase, and telophase (PMAT).

Prophase= PREPARE for division, Prophase= PREPARE for division, chromosome PRESENTchromosome PRESENT

• Chromatin begins to Chromatin begins to condensecondense and and c’some becomes visible. c’some becomes visible.

• Spindle fibers Spindle fibers formform

Prophase (cont.)Prophase (cont.)• Nuclear membrane dissolvesNuclear membrane dissolves• Microtubules form mitotic spindleMicrotubules form mitotic spindle• Kinetochore fibers and polar fibers Kinetochore fibers and polar fibers

attach to attach to centromerescentromeres

Metaphase-in MIDDLEMetaphase-in MIDDLE• Spindle fibers align the chromosomes Spindle fibers align the chromosomes

in the center or equator of the cellin the center or equator of the cell

• Helps to ensure each Helps to ensure each new nucleus will new nucleus will receive one copy receive one copy of each chromosome.of each chromosome.

Anaphase-Chromatids APARTAnaphase-Chromatids APART• Chromatids Chromatids separateseparate and move to and move to

opposite sidesopposite sides

• Spindle fibers break downSpindle fibers break down

• Once separate they are called Once separate they are called chromosomeschromosomes

Telophase-almost TWTelophase-almost TWO cellsO cells• Chromosomes arriveChromosomes arrive at opposite at opposite

polespoles

• Nuclear envelope re-forms around Nuclear envelope re-forms around daughter nuclei. daughter nuclei.

• Chromosomes uncoilChromosomes uncoil

• Spindles disappearSpindles disappear

Cytokinesis in Animal CellsCytokinesis in Animal Cells• Cytoplasm is Cytoplasm is ppinchedinched (cleavage furrow) into (cleavage furrow) into

two daughter cellstwo daughter cells

PlantsPlants• In plant cells, In plant cells,

the rigid wall the rigid wall requires that a requires that a cell platecell plate be be synthesized synthesized betweenbetween the the two daughter two daughter cells. cells.

Meiosis - Meiosis - formation formation

of gametesof gametes

Sexual ReproductionSexual Reproduction• Sex cells divide by Sex cells divide by meiosis meiosis to produce haploid to produce haploid

gamete (half the number of chromosomes)gamete (half the number of chromosomes)

• GametesGametes will join & fertilize will join & fertilize

• Meiosis produces 4 gametes that are Meiosis produces 4 gametes that are slightly slightly differentdifferent in genetic makeup from each other in genetic makeup from each other

• Two gametes join to form Two gametes join to form 11 zygotezygote

• Meiosis IMeiosis I Reduces number of Reduces number of chromosomes by half chromosomes by half (diploid to haploid) PMAT I’s (diploid to haploid) PMAT I’s – separate homologous pairs– separate homologous pairs

• Meiosis IIMeiosis II: Separates the : Separates the sister chromatids PMAT II’ssister chromatids PMAT II’s

Meiosis IMeiosis I

Meiosis IIMeiosis II

• Prophase I:Prophase I:

–Synapsis (pairing of Synapsis (pairing of homologous c’somes)homologous c’somes)

–When crossing-over happens When crossing-over happens (genetic recombination)(genetic recombination)

• Crossing overCrossing over: during Meiosis I : during Meiosis I Homologous pairs form Homologous pairs form tetradstetrads, cross , cross over and separate into individual over and separate into individual chromosomeschromosomes

• Homologous c’somes exchange Homologous c’somes exchange genetic materialgenetic material

• Important for genetic diversityImportant for genetic diversity

Prophase IProphase IEach tetradEach tetrad

has twohas two

chromo-chromo-

somes &somes &

fourfour

chromatidschromatids

MeiosisMeiosis• Spermatogenesis: production of sperm Spermatogenesis: production of sperm

cells cells

• Oogenesis: production of egg cellsOogenesis: production of egg cells

Comparing Meiosis & MitosisComparing Meiosis & MitosisGenetic identity of progenyGenetic identity of progeny

MitosisMitosis • IdenticalIdentical daughter daughter

cellscells

• diploid diploid

• 1 cell 1 cell 2 2

Meiosis Meiosis • Daughter cells have Daughter cells have

new assortment of new assortment of parental parental chromosomeschromosomes

• Chromatids Chromatids not not identical; crossing identical; crossing overover

• Diploid to haploidDiploid to haploid

• 1 cell 1 cell 4 4

Sexual ReproductionSexual Reproduction• Formation of offspring through meiosis Formation of offspring through meiosis

and the union of a sperm and an egg and the union of a sperm and an egg (zygote)(zygote)

• Offspring are genetically different from Offspring are genetically different from parentsparents

Independent AssortmentIndependent Assortment• Anaphase I – homologous Anaphase I – homologous

chromosomes separate from each otherchromosomes separate from each other

• Mendel figured this outMendel figured this out