1. Meiosis Mr. Colosi’s Biology Class

2. Definition  The successful division of a diploid (2N) eukaryotic cell that results in four haploid (N) progeny cells (the gametes in animals).  Each resulting cell has half the genetic material of the original call.  Occurs only in sexually reproducing organisms

3. Meiosis I and Meiosis II  Two cell divisions take place during meiosis.  In meiosis I, one diploid parent cell divides into two haploid cells (each chromose contains two chromatids).  In meiosis II, the two haploid cells divide into four haploid cells (each chromosome contains one chromatid).

4. Steps of Meiosis I Prophase I  Chromatin condenses into chromosomes.  Chromosomes are made up of a pair of chromatids.  Homologous chromosomes pair up  Crossing-over occurs in this step Metaphase I  Chromosomes line up at the middle (equator) of the cell.  Microtubules attach to the center of each chromosome. Anaphase I  Microtubules pull the pairs of homologous chromosomes apart. Telophase I  Cell splits into two daughter cells

6. Steps of Meiosis II Prophase II, Metaphase II, Anaphase II, & Telophase II  Follow the same steps as meiosis I  At the end of telophase II, there are four haploid cells. These cells are the gametes.

7. Genetic Diversity  When the chromosomes (maternal and paternal) are segregating, crossing-over takes place.  This is what creates the genetic variation that makes everyone different.

8. Meiosis Video http://www.youtube.com/watch?v=D1_- mQS_FZ0

9. Resources Crossing Over. Retrieved from http://www.phschool.com/science/biolo http://www.phschool.com/science/biolo gy_place/labbench/lab3/crossovr.html Meiosis. Retrieved from http://alenamedina.synthasite.com/meiosis.php http://alenamedina.synthasite.com/meiosis.php Meiosis. Retrieved from http://www.phschool.com/science/biolo gy_place/biocoach/meiosis/overview.html Meiosis. Retrieved from http://www.youtube.com/watch?v=D1_-mQS_FZ0 The Phases of Meiosis. Retrieved from http://www.brown.edu/Courses/BI0032/gentherp/phaseIBl 1.htm