Katie Hughes, David Suarez, Abi Lawrence, Taylor Edwards and Katelynn Granger 4.2.1: State that meiosis is a reduction division of a diploid nucleus to form haploid nuclei. Called reduction division because the daughter cells have only half of the number of chromosomes as the parent cell Purpose: To produce gametes to facilitate sexual reproduction Result: Four haploid cells OVERVIEW: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter28/ani mation__stages_of_meiosis.html Spilt into 2 parts: Meiosis I Prophase Metaphase Anaphase Telophase Meiosis II Prophase Metaphase Anaphase Telophase Haploid-a cell having half the number of chromosomes than a somatic cell Somatic cell- normal body cell gamete- sex cell (sperm or egg cell) Chiasmata-the site at which crossing over takes place. The process of crossing over Interphase Cell growth and DNA replication (review--before meiosis I) Prophase I Chromosomes condense Homologous chromosomes pair up and crossing over occurs (the point of cross over is known as the chiasmata) Nuclear membrane disintegrates and the centrioles travel to the poles of the cell Metaphase I Microtubules form a spindle and the spindle fibers attach to the centromeres of the chromosomes Pairs of homologous chromosomes align along the metaphase plate Anaphase I Spindle fibers shorten and pull paired chromosomes in opposite directions Paired homologous chromosomes separate and pulled to opposite poles (sides) so that each pole contains one chromosome of each pair. Telophase I A nuclear membrane forms around the chromosomes at each pole and chromosomes uncoil Spindle fibers disintegrate The cell undergoes cytokinesis to form two daughter cells (two haploid cells) At the end of telophase I the cells may enter a short interphase period or proceed directly to meiosis II DNA is not replicated Mostly the same!!! Except this time it involves half the number of chromosomes as Meiosis I Prophase II Metaphase II SAME Anaphase II No crossing over (chiasma) Separation of sister chromatids, instead of homologous chromosomes Telophase II SAME RESULT: FOUR HAPLOID DAUGHTER CELLS. http://www.phschool.com/science/biology_place/biocoach/meiosis/mei2a ni.html http://ww w.johnkyrk. com/meiosi s.html 10.1.2 Outline the formation of chiasmata in the process of crossing over New combinations of genes within chromosomes are possible through this process Can occur between any non-sister chromatids During prophase I, chromatids are close together, so parts of each chromatid overlap, break at the chiasmata and reattach to the other chromatid Sister chromatids a, b, c and d (b and c end up as new combinations called recombinants 10.1.3 Explain how meioisis results in an effectively infinite genetic variety in gametes through crossing over in prophase I and random orientation in metaphase I The number of chiasmata, or points of crossing over, can differ…..infinite variety!! 10.1.4 States that any one of a pair of characteristics may combine with either of another pair. So, two characteristics must be on different chromosomes Since any combination of chromosomes is possible in metaphase I, any one pair of characteristics may combine with either of another pair Takes place within somatic (body) cells Results in 2 daughter cells Mother cell can be haploid of diploid Is preceded by a S-phase No homologous pairing of chromosomes Genotype of daughter cells are identical to mother cells •Takes place within gametes (sex cells) •Results in 4 haploid gametes •Mother cell is diploid •Only meiosis I preceded by a S phase •During prophase I, homologous chromosomes pair up •Meiotic products differ in their genotype from the mother cell Works Cited "Chromosomes Crossing Over." Sciencelearn. University of Waikato, 8 June 2011. Web. 14 Feb. 2012. <http://www.sciencelearn.org.nz/Contexts/Uniquely-Me/Sci-Media/Images/Chromosomescrossing-over>. Farabee, M.J. "CELL DIVISION: Meiosis..." Estrella Mountain Community College. 18 May 2010. Web. 10 Feb. 2012. <http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookmeiosis.html>. Griffiths, Anthony J. F. An Introduction to Genetic Analysis. New York: W.H. Freeman, 2000. Print. Hill, McGraw. "Stages of Meiosis." Highered.mcgraw-hill.com. McGraw Hill. Web. 10 Feb. 2012. <http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio19.swf::Stages%20of %20Meiosis>. "IB Biology Notes - Meiosis." IB Guides - Free International Baccalaureate Study Guides, Notes, Videos and Powerpoints. Web. 10 Feb. 2012. <http://www.ibguides.com/biology/notes/meiosis>. Khara, Kanika. "Difference Between Mitosis and Meiosis." Buzzle Web Portal: Intelligent Life on the Web. Buzzle. Web. 14 Feb. 2012. http://www.buzzle.com/articles/difference-between-mitosis-and-meiosis.html . Kyrk, John. "Meiosis = Double Cell Division." Communicating at an Unknown Rate. 2012. Web. 14 Feb. 2012. <http://www.johnkyrk.com/meiosis.html>. Peeters, Weem Minka., Christopher Talbot, and Anthony Mayrhofer. Biology. Melton: Ibid, 2007. Print. "Phases of Meiosis | Biology." Khan Academy. Web. 10 Feb. 2012. <http://www.khanacademy.org/video/phases-of-meiosis?topic=biology>.