Cell Division You started as one cell, but now you are trillions and trillions of cells all genetically identical to that first one.

Let’s Review… Cell Cycle and Mitosis

What are the 3 stages of the cell cycle? Partner A: The 3 stages of the cell cycle are____________. Partner B: I agree/disagree because _________________.

Interphase 98% to % of the cells life cycle This is when the cells do the job they are meant to do. But there are things that the cell does to get ready for the next Mitosis.

Interphase -broken into 3 different parts: 1. G 1 - First Growth The cell grows in size and increases # of organelles 2. S - Synthesis DNA replicates during this time Happens rapidly 3. G 2 - Second Growth Increase the size of the cell again and increase the # of organelles again

What are the 4 stages of mitosis? Partner B: The 4 stages of mitosis are__________. Partner A: I agree/disagree because _______________.

Mitosis 4 stages: 1. Prophase: The Centrioles begin to move apart. Chromosomes thicken 2. Metaphase: The centrioles are at the “poles” of the cell The chromosomes line up in the middle of the nucleus The Nuclear membrane disappears 3. Anaphase: The Chromosomes are pulled toward the centrioles by spindle fibers 4. Telophase: The nucleus begins to reform and the cell begins cytokinesis

Cells divide in two different stages: First – Mitosis ( my-`toe-sis ) - Dividing the Nucleus. Second – Cytokinesis (Sye-toe-kin-E-sis) - Dividing the rest of the cell. How do you divide the nucleus? You tear it in two!!

How many Chromosomes are in each of your cells? 46 individual ones - (23 pairs) Diploid Cells (2n) A cell containing a full set of chromosomes; somatic or body cells Haploid Cells (n) A cell containing half a set of chromosomes; gametes or sex cells Homologous Chromosomes – Homologous Chromosomes – Chromosomes that have the same length and gene locations; one from mom and one from dad.

The process by which two haploid gametes combine to form a new diploid cell is called fertilization.

Meiosis: The process of dividing a diploid cell to create haploid sex cells called Gametes Gamete - sperm or egg Goes through TWO cell divisions. Starts with 1 parent cell and ends up with 4 genetically different daughter cells.

Meiosis 1 Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Interphase 1 Cell goes from 46 to 92 Chromosomes Cross over occurs Parts of “sister” chromosomes may exchange sections; this allows for genetic variation Chromosomes line up Chromosomes pull apart 2 cells with 46 individual chromosomes but not identical

Meiosis 2 NO ITERPHASE!! Prophase 2 Begins again with the two 46 chromosomes cells Metaphase 2 Same as Meiosis 1 Anaphase 2 Same as Meiosis 1 Telophase 2 & Cytokinesis Creation of 4 completely individual cells with 23 chrosomes each

Crossing over in prophase I of meiosis also allows for greater genetic variation within a species. How the chromosomes line up in metaphase I of meiosis is a random process that means every gamete created will be genetically different from the parent cell and from each other. Genetic Variation

Why is genetic variation important? Partner A: I think genetic variation is important because___________. Partner B: Genetic variation is also important because _____________.

Please take the last few minutes of class to look over your homework. Finish answering any questions you skipped and fix any you answered incorrectly. When you are finished, turn it in to Mrs. Fletcher.