Mitosis & Meiosis

Cell Cycle G1 (Gap 1)- cells carry out normal metabolic activities for day to day functions.

S (Synthesis)- DNA is replicated (duplicated, copied).

G2 (Gap 2)- cell prepares for cell division by doubling cell organelles.

MitosisA stage of the cell cycle that involves the

division of the nucleus into two new nuclei that contain identical copies of the genetic information.

Mitosis is divided into 4 stages based on the cellular events: Prophase, Metaphase, Anaphase, Telophase. (PMAT)If you include Interphase (IPMAT – I phoned

mom and talked)

Functions of Mitosis1. Growth2. Repair regenerate damaged tissues.3. Regeneration of entire body parts simpler

organisms. 4. Maintenance of the body.

Mitosis and cytokinesis occur in our body cells (aka somatic cells)

InterphasePeriod of growth & developmentHereditary information (DNA) copied (replicated / duplicated)

Cells that do not divide (nerves) are always in interphase

ProphaseDNA begins to shorten & thicken

Now called chromatids/chromosomes

Centromeres formNuclear membrane breaks apartSpindle fibers begin to form

MetaphaseChromatids / chromosomes line upCentromere attaches to spindle fibers

AnaphaseCentromeres divideSpindle fibers shortenSister chromatid pairs separate – move to opposite ends of the cell.

TelophaseSpindle fibers begin to disappear Chromosomes begin to uncoilNuclear membrane starts to re-formCell plate (plant cell) or Cleavage furrow (animal cell) becomes highly noticeable.

Cytokinesis (Cell Cutting)The division of the cytoplasm is know as cell

cutting. This signals the end of Mitosis. After the cells membrane or wall forms a

complete new barrier between the two sister cells. We would say cytokinesis has just occurred.

Interphase

                                                            

Prophase

                                                            

Metaphase

                                                            

Anaphase

                                                            

Telophase

                                                            

Interphase

                                                            http://biology.nebrwesleyan.edu/benham/mitosis/

Mitosis Animation

http://www.johnkyrk.com/mitosis.html

Results of MitosisDivision of nucleus

Nuclei are identical to each otherSame number & type of chromosomes

A type of reproduction - fission, budding, and regeneration - in

which a new organism is produced from one parent and has DNA

identical to the parent organism.

Asexual Reproduction

Offspring produced from one organism

Hereditary information is identical

Mitosis is one form of asexual reproduction

Meiosis

A type of reproduction in which two sex cells, usually an egg and a sperm, join to form a zygote, which will develop into a new

organism with a unique identity.

Meiosis The nucleus divides twice

Meiosis IMeiosis II

Final Product will be 4 cells from one parent that contains ½ the original amount of chromosomes as the parent.

InterphaseSame as in Mitosis.Normal life cycle functions of the cellDivided into 3 stages:

G1 (Gap 1)- Growth and developmentS (Synthesis Phase) - DNA is duplicatedG2 (Gap 2)- Organelles double in preparation

for separation

Prophase I

DNA begins to shorten & thickenNow called chromatids/chromosomes

Centromeres formNuclear membrane breaks apartSpindle fibers begin to formCROSSING OVER may occur.

Metaphase ICopied chromatids / chromosomes line up in middle of cell in HOMOLOGOUS PAIRS

Centromeres attach to spindle fibers

Anaphase IHomologous chromosomes separate and move to the poles.

Chromatid pairs are NOT pulled apartThey DO NOT separate

Chromatids move to ends of cell

http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/anaphase-I/anaphase-i.gif

Telophase IMay or May Not occur.If it does:

Normal telophase, X-somes uncoil, nucleus appears, cell divides

No further replication of hereditary material

http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/telophase-I/telophase-I.gif

- There are now two cells with each cell carrying only ½ the original chromosome number. (HAPLOID)

- Cells carry one duplicated copy of a single chromosome.They do not normally or necessarily carry

the same genetic information as the parent cell or the sister chromatid.

Because the chromosome number decreases this phase of meiosis is known as Reduction Division.

Prophase IISimilar to mitosis

Starts with TWO cells instead of oneSpindle fibers appearNucleus disappears (if reformed)

http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/prophase-II/prophase-II.gif

Metaphase IIDuplicated chromatid / chromosomes line up in middle of cell

Spindle fibers attach to centromeres

http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/metaphase-II/metaphase-II.gif

Anaphase IICentromere divides

Chromatids separate & move to ends of cellChromatids are now individual chromosomes

http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/anaphase-II/anaphase-II.gif

Telophase IISpindle fibers disappearNuclear membranes form at each end of cell

Cells divide Results in 4 cells

Each with ½ the original number of chromosomes

http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/telophase-II/telophase-II.gif

http://www.johnkyrk.com/meiosis.html

In summary:MeiosisTwo cells form during meiosis IIn meiosis II, both of these cells form two cellsThe two divisions of the nucleus result in four

sex cells (gametes)Each has one-half the number of

chromosomes in its nucleus that was in the original nucleus