[Remember: Mitosis happens in my toesies]

Purposes of cell division Increase the number of cells for growth and repair of worn out tissues (mitosis) Transmit genetic information (DNA) to other cells We will study transmitting DNA to other generations later: Reproduction and heredity

Mitosis: One cell becomes two Each daughter cell gets exactly the same DNA. Mitosis goes on in all parts of a Eukaryotes body. Prokaryotes use a different method — “Binary fission” to divide.

Chromosomes are coiled strands of instructions (DNA) This is a chromosome in the “mother” cell This is also called a chromosome, but it has doubled itself so that there is one copy for each “daughter” cell. This is an actual image of a chromosome that has both copied itself and coiled up into this nice fluffy shape. These are the “daughter” cells and each has its own copy of all the DNA—They are clones of the “mother” cell and identical to each other in all ways.

Clearing up the confusion! Remember, even though it is doubled they still call it a chromosome! The two copies are called sister chromatids

It’s the same DNA; just at different stages of the cell cycle. Here the DNA is not as coiled so the ENTIRE nucleus is colored when the DNA is stained. Here the DNA is coiled tighter so only the chromosomes are colored and visible.

Chromosomes and Genes A gene is a short length of DNA on a chromosome which controls an inherited characteristic of the organism (It is the instruction for a single protein) A chromosome carries a lot of genes (it is more like an instruction book) gene controlling skin colour gene controlling tongue rolling chromosome gene controlling eye colour gene controlling blood group

Our Chromosomes: From uncoiled to coiled

Each Human cell has 46 chromosomes 22 pairs are essentially identical in both sexes One from Mom, one from Dad. Autosomes The 23rd pair is different in males (They have an X and a Y chromosome) and females (they have two X’s). Sex chromosomes. Other species have different numbers of chromosomes: Horse - 64 A fern species - 1200 Flatworm - 16 Fruit Fly - 8 Male ants - 1

2 major parts of the cell cycle The cells grow, lots of extra proteins are made, and organelles (such as the mitochondria) and DNA replicate to prepare for cell division. The cell divides (mitosis) resulting in two identical daughter cells (clones).

The Cell Cycle Cells are either Growing (G phase) Synthesizing new DNA (S phase) 0r dividing by Mitosis (M phase) M phase has four parts: Prophase, Metaphase, Anaphase and Telophase. The G and the S phases are collectively called the Interphase

Interphase (Resting and growing stage) Chromosomes cannot be seen. Cells grow. Chromosomes duplicate. How do the chromosomes duplicate?

nuclear membrane disappearing Prophase nuclear membrane disappearing chromatids centromere Chromosomes condense and become visible Each chromosome consists of two identical sister chromatids. homologous chromosomes

Metaphase Chromosomes line up at the equator (centre of the cell) Spindles are formed to attach to the center of each chromosome

Anaphase Sister chromatids separate as individual chromosomes They move apart towards the opposite poles

nuclear membrane forming Telophase nuclear membrane forming Chromosomes gradually disappear Nuclear membrane is formed around each set of chromosomes

Summary of Mitosis Summary of Mitosis

Prophase In prophase, the cell begins the process of division and chromosomes condense.

Metaphase In metaphase the chromosomes line up on the equator of the cell

Anaphase In anaphase, the centromeres divide. Each half of the cell gets a single chromatid.

Telophase In telophase the chromosomes are at the poles of the cell. Then the cytoplasm divides into 2 separate cells.

Summary of Mitosis Prophase: Chromosomes condense and are visible Nuclear membrane disappears Metaphase Chromosomes lined up on equator of cell Anaphase Chromosomes divide and are pulled to opposite poles of the cell Telophase Chromosomes disappear and Cytoplasm divided into 2 cells New nuclear membranes are also formed.

Cancer Cancer is a disease of uncontrolled cell division. It starts with a single cell that loses control of the cell cycle due to a DNA mutation in gene for a protein that controls that cycle. That cell starts dividing without limit, and eventually can kill the host.

Can you identify the different stages of mitosis from the diagram below? anaphase interphase telophase metaphase prophase

A Review At which stage is there most protein production? At which stage do the chromosomes line up at the cell equator? At which stage do the chromosomes become visible? At which stage do the chromosomes replicate? At which stage does the nuclear membrane re-appear? At which stage do the Sister Chromatids separate? At which stage does the nuclear membrane disappear? Is Chromosome 13 from Mom identical to C13 from Dad? What is a Gene? Are the genes on Sister Chromatids identical?