Cell Division

Mitosis vs. Meiosis

….the battle continues

Mitosis• Type = Asexual

reproduction

• Growth, maintenance, and repair

• Takes place in somatic (body) cells

http://images.google.co.za/imgres?imgurl=http://static.guim.co.uk/sys-images/Guardian/Pix/pictures/2007/08/26/Embryo1.gif&imgrefurl=http://www.guardian.co.uk/science/2007/aug/26/theobserversuknewspages.genetics&h=276&w=460&sz=101&hl=en&start=18&um=1&usg=__iH23ufmESehR6vOpdRQtLaNoyww=&tbnid=sgf9d9yu_4htVM:&tbnh=77&tbnw=128&prev=/images%3Fq%3Dembryo%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN

Cell Cycle

• Interphase Cells are in interphase 90% of the time.

– G1- growth– S - chromosome

replication– G2- Prepare for mitosis

• Mitosis (nuclear division)

• Cytokinesis (cytoplasmic division)

Overview of Mitosis

Mama Cell=2n (diploid)

Daughter cell= 2n

(diploid)

Daughter cell= 2n

(diploid)

Interphase (pre game show)

• Chromosomes are copied (# doubles)

• Chromosomes appear as threadlike coils (chromatin) at the start, but each chromosome and its copy(sister chromosome) change to sister chromatids at end of this phase

PROPHASECENTRIOLES APPEAR AND MOVE TO OPPOSITE ENDS OF THE CELL

Spindle fibers form between centrioles

METAPHASE

• Chromosomes “meet” in the middle. Spindle fibers attach to the centromere of each chromosome.

ANAPHASE

• Sister chromatids separate from each other and are “pulled” to opposite ends of the cell.

Telophase• Cell plate forms and cell membrane

begins pinching in= “cleavage.”• Chromosomes look like threads

(chromatin) again. Nuclear envelope forms again.

Cytokinesis

• Division of the cytoplasm• Cell membrane completely pinches

off.• Cycle starts again.

Rounds of Cell Division

• One

Number of daughter cells

• Two, each identical to each other and the parent.

Meiosis

Meiosis• Type: Sexual

Reproduction

• Purpose: To create haploid gametes

• Takes place in gametes (sex cells/egg and sperm cells)

Meiosis• Types of cells that undergo

meiosis: Gametes (sex cells)– Egg and sperm

Meiosis: Overview

Parent Cell: diploid= 2n

After Meiosis I

After Meiosis II

Daughter Cells:Haploid= n ; and all genetically different from eachother and parent cell

???

Why would it be important for the gametes to contain half as many chromosomes

as a somatic cell?

Meiosis IProphase I: Crossing Over occurs to create genetic variability.

Meiosis I: Metaphase I

• Homologous chromosomes line up in the middle different from mitosis!

Meiosis I: Anaphase I

• Chromosomes pull apart

Meiosis I: Telophase I

Meiosis II

•2nd round of division

Meiosis II: Prophase II•2 cells now

•Centrioles appear and move to opposite ends

Meiosis II: Metaphase II

• Chromosomes line up in the middle

Meiosis II: Anaphase II•Sister chromatids pull apart and move to opposite ends

DRAW IT YOURSELF

Telophase II

Chromosome number in Meiosis

• Mother cell-2n (Diploid)

• Daughter cells- n (Haploid)

Round of cell division

• Two

• Illustrate mother cell with four chromosomes (2n) and daughter cells with two chromosomes (n) in each. Make sure to include replication before meiosis I.

Number of daughter cells

• Four

Let’s compare!

• http://www.teachersdomain.org/resources/tdc02/sci/life/gen/mitosis/index.html

Ticket to the Lab

• Name 3 key differences between mitosis and meiosis on your foldable.