Mitosis and MeiosisMitosis and Meiosis

Differences in Human Cell Differences in Human Cell TypesTypes

Somatic CellsSomatic Cells

-“regular”-“regular”

-diploid (46 -diploid (46 chromosomes)chromosomes)

-Identical DNA -Identical DNA throughout bodythroughout body

Gamete-Gamete-

-sex cells-sex cells

-haploid-haploid

-sperm and eggs-sperm and eggs

MitosisMitosis

Division of somatic Division of somatic cellscells

Necessary for Necessary for tissue growth or tissue growth or repairrepair

5 steps5 steps– DNA must be DNA must be

duplicatedduplicated– 4 step process to 4 step process to

divide DNAdivide DNA

InterphaseInterphase

Longest stage of Longest stage of cell’s life cyclecell’s life cycle

Part of the cell Part of the cell cycle in which DNA cycle in which DNA replication occursreplication occurs

Towards the end, Towards the end, the cell prepares the cell prepares for divisionfor division

ProphaseProphase

Cell with 2 sets of Cell with 2 sets of DNADNA

Chromatin (loose Chromatin (loose DNA) condenses DNA) condenses into chromosomesinto chromosomes

First step in which First step in which chromosomes are chromosomes are visible.visible.

MetaphaseMetaphase

Chromosomes line Chromosomes line up on “equator” of up on “equator” of cellcell

Spindle Fibers Spindle Fibers attach to attach to centromere (center centromere (center of chromosome) of chromosome) from centrioles at from centrioles at each poleeach pole

AnaphaseAnaphase

Chromosomes are Chromosomes are split into two (each split into two (each still identical) and still identical) and pulled towards pulled towards opposite poles.opposite poles.

TelophaseTelophase

Daughter cells Daughter cells separate by separate by pinching apartpinching apart

Nuclear division Nuclear division completecomplete

Finishes with Finishes with cytokinesis cytokinesis (division of (division of cytoplasm)cytoplasm)

After MitosisAfter Mitosis

Two identical Two identical daughter cellsdaughter cells

Have identical Have identical (diploid) genome(diploid) genome

CancerCancer

Uncontrolled growth of cellsUncontrolled growth of cells

Proteins called oncogens and Proteins called oncogens and protooncogens usually control cell cycleprotooncogens usually control cell cycle

If they get damaged, cell cycle is If they get damaged, cell cycle is uncontrolleduncontrolled

MeiosisMeiosis

Cell division in Cell division in gametesgametes

Same stages as Same stages as mitosismitosis

In meiosis, DNA In meiosis, DNA undergoes another undergoes another divisiondivision

Meiosis contd.Meiosis contd.

Leads to 4 haploid Leads to 4 haploid daughter cells (23 daughter cells (23 chromosomes each) chromosomes each) Why?Why?

In females, 1 of the In females, 1 of the daughter cells is daughter cells is retained as ovumretained as ovum

In males, all 4 become In males, all 4 become nucleus of spermnucleus of sperm

When Meiosis goes wrong..When Meiosis goes wrong..

Non-disjunction-Non-disjunction-both chromosomes both chromosomes pulled into one pulled into one daughter cell, daughter cell, resulting in 47 resulting in 47 chromosomes after chromosomes after fertilizationfertilization

ResultsResults

Downs syndrome – Downs syndrome – trisomy 21trisomy 21

Edwards syndrome Edwards syndrome – trisomy 18– trisomy 18

Patau’s syndrome – Patau’s syndrome – trisomy 13trisomy 13