How do little elephants grow up to be BIG elephants? How does a little elephant come to be?

CELL DIVISION!!

There are two types of cell division. Mitosis – when an organism is growing, repairing or replacing cells EX: skin cells replacing dead skin cells Meiosis – when it’s time to reproduce an organism EX: when you were created!

Meiosis or Mitosis? A) A snake sheds its skin. B) My dog just had puppies. C) You grew four inches in the last 2 years.

MITOSIS

Mitosis Cycle Interphase Prophase Metaphase Anaphase Telophase http://www.youtube.com/watch?v=NR0mdDJMHIQ&feature=related Interphase Prophase Metaphase Anaphase Telophase Cytokinesis

Interphase The cell prepares to divide by copying its DNA

Interphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Prophase The chromatin in the nucleus condenses and forms chromosomes. Centrioles appear at the poles of the cell. The nuclear envelope breaks down.

Prophase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Metaphase The centrioles attach spindle fibers to the centers of each chromatid (a pair of chromosomes) The chromatids are being pulled in both directions, so they end up lined up across the center of the cell.

Metaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Anaphase 3rd step in Mitosis The chromatids split up; half moving toward one pole and the other half moving toward the other pole. The cell begins to stretch.

Anaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Telophase Two new nuclear envelopes form. The chromatids loosen up and appear as chromatin again

Cytokinesis The cell membrane pinches into two ‘daughter cells’ that are exactly the same as the ‘parent cell.’

Animal Mitosis -- Review Interphase                                                              Prophase                                                              Metaphase                                                              Anaphase                                                              Telophase                                                             

Plant Mitosis -- Review Interphase                                                              Prophase                                                              Metaphase                                                              Anaphase                                                              Telophase                                                             

Cell Cycle

MEIOSIS

Meiosis Interphase Meiosis is preceded by interphase. The chromosomes have not yet condensed. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

Meiosis Interphase The chromosomes have replicated, and the chromatin begins to condense. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

Meiosis Prophase I The chromosomes are completely condensed. In meiosis (unlike mitosis), the homologous (same) chromosomes pair with one another http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

Meiosis Metaphase I The nuclear membrane dissolves and the chromosomes attach to the spindle fibers. They are preparing to go to opposite poles. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

Meiosis Anaphase I The chromosomes move to opposite ends of the cell. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

Meiosis Telophase I & Cytokinesis The cell begins to divide into two daughter cells. It is important to understand that each daughter cell can get any combination of maternal and paternal chromosomes. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

Meiosis Prophase II The cell has divided into two daughter cells. These cells are diploid, they have a full set of chromosomes. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

Meiosis Metaphase II As in Meiosis I, the chromosomes line up on the spindle fibers. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

Meiosis Anaphase II The two cells each begin to divide. As in Meiosis I, the chromosomes move to opposite ends of each cell. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

Telophase II & Cytokinesis With the formation of four cells, meiosis is over. Each of these daughter cells have half the chromosomes of parent cells, which is called, haploid. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

Meiosis is basically the same as mitosis, BUT it happens twice and it ends up with four cells at the end. AND the four ‘daughter cells’ only have half of the chromosomes that the ‘parent cell’ had.

Mitosis Vs. Meiosis Mitosis Divides body cells Same number of chromosomes as original cell (diploid) The 2 daughter cells at the end will have 46 chromosomes (23 pair) Meiosis Divides sex cells End up with ½ of the chromosomes of original cell (haploid) The 4 daughter cells at the end will each have 23 chromosomes