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:  hill.com/sites/ /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  No crossing over (chiasma)  Metaphase II  SAME  Anaphase II  Separation of sister chromatids, instead of homologous chromosomes  Telophase II  SAME RESULT: FOUR HAPLOID DAUGHTER CELLS. ni.html

w.johnkyrk. com/meiosi s.html

 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

 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!!

  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 Web. 14 Feb Farabee, M.J. "CELL DIVISION: Meiosis..." Estrella Mountain Community College. 18 May Web. 10 Feb Griffiths, Anthony J. F. An Introduction to Genetic Analysis. New York: W.H. Freeman, Print. Hill, McGraw. "Stages of Meiosis." Highered.mcgraw-hill.com. McGraw Hill. Web. 10 Feb "IB Biology Notes - Meiosis." IB Guides - Free International Baccalaureate Study Guides, Notes, Videos and Powerpoints. Web. 10 Feb Khara, Kanika. "Difference Between Mitosis and Meiosis." Buzzle Web Portal: Intelligent Life on the Web. Buzzle. Web. 14 Feb Kyrk, John. "Meiosis = Double Cell Division." Communicating at an Unknown Rate Web. 14 Feb Peeters, Weem Minka., Christopher Talbot, and Anthony Mayrhofer. Biology. Melton: Ibid, Print. "Phases of Meiosis | Biology." Khan Academy. Web. 10 Feb