CELL DIVISION Turn in pg. 15 in the Resource Book.

CELL DIVISION Necessary for GROWTH and REPAIR Two major processes of cell division. Left side – MITOSIS Right side - MEIOSIS

MITOSIS Occurs in body cells. Basically all your cells except the sex cells. Contains a full set of chromosomes. (2n) Diploid. The (n) value depends on the organism. In humans, (n) is equal to 23. Results in two identical daughter cells.

Mitosis has 5 stages Interphase Prophase Metaphase Anaphase Telophase

Interphase Chromosomes form thin strands called CHROMATIN which has DNA in structures called NUCLEOSOMES. Can be divided into three phases: G1, S, and G2. Cell spends most of its time in interphase

Prophase The CENTRIOLE divides and aids in spindle formation. The chromatin reforms into chomosomes.

What is a chromosome?

Metaphase Chromosomes line up at the middle.

Anaphase The CHROMOSOMES separate. The centrioles pull the chromosomes to opposite ends of the cell.

Telophase The SPINDLE FIBERS and CENTRIOLES disappear. Result in a DIPLOID (2n) number of chromosomes. Process of Cytokinesis.

MEIOSIS Occurs in sex cells (egg and sperm) Contains a half set of chromosomes. (n) Haploid. Results in four different cells. Germ cells unite to form a ZYGOTE (fertilized egg)

Meiosis has 8 stages Meiosis I – CHROMOSOMES carry genetic information and separate. They line up as TETRADS. (which are pairs of chromatids)

Meiosis has 8 stages Meosis II – The CHROMATID PAIRS divide. FOUR cells are finally formed. Each cell is a HAPLOID (n)

Meiosis In females, the process of meiosis is called OOGENESIS. It results in one large egg cell and three small polar bodies. In males, the process of meiosis is called SPERMATOGENESIS. It results in four equal sperm cells.

ASEXUAL CELL DIVISION The two major types of asexual cell division are BUDDING and BINARY FISSION. Binary fission is the splitting INTO TWO where budding is when the young grow off the adult. Both result in a IDENTICAL DAUGHTER CELLS. Similar as in Mitosis.

What is a zygote? A zygote is a fertilized egg. A zygote goes through stages of cleavage. You will need to know the following stages: 1. BLASTOMERE – four cell stage

Stages of Cleavage cont. 2. BLASTULA – A hollow ball made out of a single layer of cells.

Stages of Cleavage cont. 3. GASTRULA – The hollow ball folds in on itself to form three layers of cells/tissues.

THREE EMBRYONIC TISSUE LAYERS 1. ECTODERM – gives rise to the skin and nervous system. 2. ENDODERM (Entoderm) – gives rise to the digestive tract. 3. MESODERM – gives rise to the muscles, bones, and blood.

ANY QUESTIONS????