Chromosomes

Chromosome Formation

Histone Proteins- Help maintain shape of the chromosome

Chromosomes-ROD Shaped structure made of DNA and Protein

Structure of a Chromosome

CENTROMERE

CHROMATIDCHROMATID

Homologous Chromosomes- Humans have 46 chromosomes

23 homologous pairs

AUTOSOMES

SEX CHROMOSOMES

Humans have 2

Male XY

Female XX

Humans Have 44 Autosomes

CHROMOSOME NUMBER

Honeybee (female) – 32

2n Chromosomes

Adder’s Tongue Fern - 1262 Common Frog - 26

Cat - 38 Maize - 20Human - 46

Does more chromosomes mean a bigger or more complicated organism?

Chromosome number does not determine complexity of organism

DIPLOID CELLS VS. HAPLOID CELLS

Diploid 2N= Contains both

autosomes in a homologous pair

Human Body Cells are Diploid

Contain 46 chromosomes and 23 pairs

Haploid 1N= Contains 1 autosome of

homologous pair

Human sex cells are Haploid

Egg and Sperm Cell

Contain 23 Chromosomes and no pairs

Mitosis vs. Meiosis

46

46 46

MITOSIS

46

23 23

23 23 23 23

MEIOSIS

HOMOLOGOUS CHROMOSOMES

Cell Division

Eukaryotes vs. Prokaryotes

Prokaryotes vs. EukaryotesCharacteristicsProkaryotes

Single celled organisms

No membrane bound nucleus or organelles

Simple and smaller

Have a cell wall

Few chromosomes

Eukaryotes Make up multicellular

organisms Have membrane bound

organelles and nucleus Complex and Larger

Many chromosomes

DNA located in the nucleus

Chromosomes coil and condense before cell division

Prokaryotic Cell DivisionProkaryotic Cell Division

• Binary fissionBinary fission• Division of prokaryotic cell into two offspring cellsDivision of prokaryotic cell into two offspring cells

Cell Division in EukaryotesCell Division in Eukaryotes

Cell Division occurs in two stagesCell Division occurs in two stages

Mitosis/MeiosisMitosis/Meiosis Division of the nucleusDivision of the nucleus Four stages (Prophase, Metaphase, Anaphase, Four stages (Prophase, Metaphase, Anaphase,

Telophase)Telophase)

CytokinesisCytokinesis Division of the cytoplasmDivision of the cytoplasm

Prokaryotic vs Eukaryotic Cell Division

Prokaryotes DNA is circular and attached to

the plasma membrane DNA does not wrap around

proteins to form chromosomes before cell division

Binary Fission(most cells) Cell membrane will develop

between the two copies of DNA Cell Doubles in size Cell membrane pinches off Cell Wall forms around new

cell membrane

Eukaryotes

Chromosomes coil and condense before cell division

Consists of 2 Divisions1)Division of the nucleus Mitosis – body

cells(Diploid Cells) Meiosis- sex cells

(Haploid cells)2) Division of the

Cytoplasm Cytokinesis

What is the same in Euk and Prok cell division? Create new cells Genetically identical DNA is copied before cell division Cytoplasm will divide

Eukaryotic Cell Division

Cell Cycle

CELL CYCLE-CELL CYCLE- Repeating set of Repeating set of events in the life of the cellevents in the life of the cell

Interphase-Interphase-longest stage in the cell cyclelongest stage in the cell cycle

G1 – Cell growth (cell grows to a mature size)G1 – Cell growth (cell grows to a mature size)

S – DNA is copied (double the amount of S – DNA is copied (double the amount of DNA)DNA)

G2 – Growth and preparation for cell divisionG2 – Growth and preparation for cell division

G0-Cells that do not divide will remain in G0 G0-Cells that do not divide will remain in G0 (occurs at the end of G1)(occurs at the end of G1)

Cell divisionCell division

Mitosis/Meiosis – Nucleus dividesMitosis/Meiosis – Nucleus divides

Cytokinesis – Division of the cytoplasmCytokinesis – Division of the cytoplasm

What triggers the cell to leave on phase What triggers the cell to leave on phase and move to the next?and move to the next?

Checkpoints = traffic signalCheckpoints = traffic signal Proteins regulate the processProteins regulate the process

Three main checkpointsThree main checkpoints G1 checkpoint(end of G1)G1 checkpoint(end of G1) G2 checkpoint (during G2)G2 checkpoint (during G2) Mitosis checkpoint (toward Mitosis checkpoint (toward

the end of mitosis)the end of mitosis)

Control of Cell Division

G1 checkpoint-Cell Growth CheckpointG1 checkpoint-Cell Growth Checkpoint Checks to see if the cell is healthy and has reached a Checks to see if the cell is healthy and has reached a

mature sizemature size Will determine if the cell will divideWill determine if the cell will divide

G2 checkpoint-DNA synthesis checkpointG2 checkpoint-DNA synthesis checkpoint DNA repair enzymes check the results of DNA replicationDNA repair enzymes check the results of DNA replication

Mitosis checkpoint-Mitosis checkpoint- If cell passes this checkpoint, the cell will exit Mitosis and If cell passes this checkpoint, the cell will exit Mitosis and

move into G1 of interphasemove into G1 of interphase

What happens if there is a mutation in one of these proteins?What happens if there is a mutation in one of these proteins?

Organelle ReviewOrganelle Review

CentrosomesCentrosomes Contain two centriolesContain two centrioles Made of microtubulesMade of microtubules Acts as anchors in cell divisionActs as anchors in cell division

Plants centosomes do not contain centriolesPlants centosomes do not contain centrioles

Mitotic Spindle fibers-Two Main typesMitotic Spindle fibers-Two Main types Kinetochore Fibers-Kinetochore Fibers- Attach from centriole to Attach from centriole to

centromere of chromosomes and assists in centromere of chromosomes and assists in movement of chromosomesmovement of chromosomes

Polar FibersPolar Fibers – Extend from pole to pole and – Extend from pole to pole and keep the shape of the cell during cell divisionkeep the shape of the cell during cell division

Organelle Review

Nuclear envelopeNuclear envelope•Double Phospholipid bilayer Double Phospholipid bilayer

surrounding nucleussurrounding nucleus•Surrounds the DNASurrounds the DNA

NucleolusNucleolus•Dense area where DNA is Dense area where DNA is

concentrated in the nucleusconcentrated in the nucleus•Ribosomes (rRNA) is synthesizedRibosomes (rRNA) is synthesized

MITOSIS Division of the nucleus Forms two identical daughter cells Four phases

Where does it occur? Somatic Cells (Body cells)

Why does it occur?Why does it occur?• Asexual reproductionAsexual reproduction• Growth and developmentGrowth and development• To replace old cells or dying cellsTo replace old cells or dying cells

ProphaseProphase

• Chromatin coils and condenses Chromatin coils and condenses into chromosomesinto chromosomes

• Nucleolus and nuclear Nucleolus and nuclear membrane break down and membrane break down and disappeardisappear

• Centrosomes appear and move Centrosomes appear and move to opposite ends of the cellto opposite ends of the cell

• Spindle Fibers appear: Spindle Fibers appear: Kinetochore fibers extend from Kinetochore fibers extend from kinetochore of each chromatid kinetochore of each chromatid to centrosome.to centrosome.

Metaphase

Metaphase = MiddleMetaphase = Middle Kinetochore fibers Kinetochore fibers

move chromosomes move chromosomes to center of the cellto center of the cell

All chromosomes All chromosomes line up in a single file line up in a single file lineline

46 chromosomes 46 chromosomes lined up in the lined up in the middle (Humans)middle (Humans)

AnaphaseAnaphase

AnaphaseAnaphase• Chromosomes separate at Chromosomes separate at

the centromere and the centromere and chromatids move to opposite chromatids move to opposite polespoles

• Chromatids are now Chromatids are now considered individual considered individual chromosomeschromosomes

TelophaseTelophase• Chromosomes are on opposite Chromosomes are on opposite

sides of the cellsides of the cell• Centrioles disappear and Centrioles disappear and

Spindle fibers disassemble and Spindle fibers disassemble and disappeardisappear

• Chromosomes unwind into less Chromosomes unwind into less tightly coiled chromatin tightly coiled chromatin

• Nuclear envelope forms around Nuclear envelope forms around each set of chromosomeseach set of chromosomes

• Nucleolus forms in each of the Nucleolus forms in each of the newly forming cellsnewly forming cells

Animation

CYTOKINESISCytokinesis-the division of the Cytokinesis-the division of the

cytoplasmcytoplasm

Animal cells:Animal cells:

Pinching inward of the cell membrane Pinching inward of the cell membrane occurs.occurs.

Called Cleavage furrowCalled Cleavage furrow

In plantsIn plants cell plate formationcell plate formation

Which stage?

Mitosis vs. MeiosisMitosis vs. Meiosis

Where do they occur?Where do they occur? Mitosis – in the body cellsMitosis – in the body cells Meiosis – in the germ cellsMeiosis – in the germ cells

Why does it occur?Why does it occur? MitosisMitosis

• Asexual reproductionAsexual reproduction• Growth and developmentGrowth and development• To replace old cellsTo replace old cells

MeiosisMeiosis• Formation of gametes (egg and sperm cells) Formation of gametes (egg and sperm cells)

that will be used in sexual reproductionthat will be used in sexual reproduction

Mitosis vs. MeiosisMitosis vs. Meiosis

46

46 46

MITOSIS

46

23 23

23 23 23 23

MEIOSIS

MeiosisMeiosis

Also known as reduction divisionAlso known as reduction division Occurs in germ cells found in the ovaries and testesOccurs in germ cells found in the ovaries and testes Produces sex cells which are haploidProduces sex cells which are haploid Occurs in two phasesOccurs in two phases

Meiosis IMeiosis I• Reduces the number of chromosomes from diploid Reduces the number of chromosomes from diploid

to haploidto haploid Meiosis IIMeiosis II

• Produces four haploid daughter cellsProduces four haploid daughter cells

Meiosis IMeiosis I

Meiosis IMeiosis IProphase IProphase I

DNA coils tightly into chromosomesDNA coils tightly into chromosomes Spindle fibers and centrosomes Spindle fibers and centrosomes

appearappear Nucleolus and nuclear envelope Nucleolus and nuclear envelope

disassembledisassemble Synapsis =Pairing of homologous Synapsis =Pairing of homologous

chromosomeschromosomes Tetrad =Pair of homologous Tetrad =Pair of homologous

chromosomes twisted around each chromosomes twisted around each other other

Crossing over may occurCrossing over may occur Genetic recombinationGenetic recombination

Meiosis IMeiosis I Metaphase IMetaphase I

• Tetrads line up along midlineTetrads line up along midline• Independent assortment occursIndependent assortment occurs

Anaphase IAnaphase I• Homologous chromosome pairs(Tetrads) are separated and Homologous chromosome pairs(Tetrads) are separated and

move to opposite poles (Independent assortment occurs)move to opposite poles (Independent assortment occurs)

Telophase ITelophase I• Chromosomes reach opposite ends of cellChromosomes reach opposite ends of cell• Spindle Fibers disappearSpindle Fibers disappear• In some cells the nuclear envelope will reappearIn some cells the nuclear envelope will reappear• Cytokinesis beginsCytokinesis begins

Meiosis IIMeiosis II

Meiosis IIMeiosis II

Prophase IIProphase II Spindle fibers form and attach to the centromere of the Spindle fibers form and attach to the centromere of the

double stranded chromosomes. (Nuclear envelope double stranded chromosomes. (Nuclear envelope will disappear if it was created)will disappear if it was created)

Metaphase IIMetaphase II Double stranded chromosomes are moved to the Double stranded chromosomes are moved to the

midline of the dividing cellmidline of the dividing cellAnaphase IIAnaphase II

Chromatids separate and move toward opposite polesChromatids separate and move toward opposite polesTelophase IITelophase II

Nuclear membrane forms and nucleolus reappears, Nuclear membrane forms and nucleolus reappears, spindle fibers and centrosomes disappear, chromatin spindle fibers and centrosomes disappear, chromatin uncoils into chromosomesuncoils into chromosomes

Cytokinesis II

Division of the cytoplasm occurs Division of the cytoplasm occurs resulting in four new cellsresulting in four new cells

Each cell contains half the original Each cell contains half the original amount of chromosomes amount of chromosomes

Mitosis vs. MeiosisMitosis vs. Meiosis

Development of Gametes in Development of Gametes in AnimalsAnimals

SpermatogenesisSpermatogenesis produces Sperm or produces Sperm or

SpermatozoaSpermatozoa produces fourproduces four

OogenesisOogenesis Cytoplasm is divided unequallyCytoplasm is divided unequally Produces one mature egg cell or OvaProduces one mature egg cell or Ova Polar bodies are the three other products of meiosis Polar bodies are the three other products of meiosis

and they will eventually degenerate.and they will eventually degenerate.