1. Tiana Hobbs and Brandon Douglas 4.2.3, 10.1-10.1.5

2. Assessment Statement 4.2.3,10.1.1,10.1.3 Outline the process of meiosis, including pairing of homologous chromosomes and crossing over, followed by two divisions, which results in four haploid cells. Describe the behavior of the chromosomes in the phases of meiosis. Explain how meiosis results in an effectively infinite genetic variety in gametes through crossing over in prophase I and random orientation in metaphaseI.

3. Overview Meiosis Involves two divisions 1 st division called Meiosis I Interphase stage before Meiosis I which includes G1, S, and G2 phases; similar to Interphase stages before Mitosis. Short Interphase stage between Meiosis I and Meiosis II

4. Phases of Meiosis

5. Prophase I- within this stage, the chromosomes are becoming visible The homologous chromosomes pair up and crossing over occurs The nuclear membrane separates and the centrioles move to the poles of the cell

6. Metaphase I Homologous chromosome pairs line up at equator of cell Spindle fibers attach to chromosomes so that one chromosome from each pair is moved to each pole.

7. Anaphase I Homologous chromosomes separated and pulled to opposite poles Unique number of chromosomes reduced to 23 from 46, although chromosomes are still composed of 2 sister chromatids. Cell prepares for Cytokinesis

8. Telophase I Each chromosome from each homologous pair are located at opposite poles Nuclear membrane reforms around each daughter nucleus Cell divides through cytokinesis

9. Meiosis II Starts with two daughter haploid cells Ends in the formation of four daughter cells, each with a haploid set of chromosomes.

10. Prophase II Two daughter haploid cells present. Nuclear membrane begins to break down Spindle fibers form

11. Metaphase II Chromosomes in each cell line up at equate of each respective cell Spindle fibers attaches to the centromeres of each chromosome

12. Anaphase II Chromosomes are divided at centromere as a result of the spindle fibers pulling each sister chromatid to opposite poles. Sister chromatids then become chromosomes

13. Telophase II Nuclear membranes form around each of the four sets of chromosomes Cell divides through cytokinesis Results in four daughter cells each with a haploid set of chromosomes.

14. Crossing Over Prophase I Forms chromatids with new combinations of alleles Recombinants are chromatids with different combinations of alleles than either parent chromatid Crossing over occurs at a random point More than one chiasma can form per homologous pair.

15. Random Orientation Metaphase I Homologous chromosomes line up at the equator in a random order Maternal or Paternal homologue can be pulled to either pole To calculate all variations you raise the number 2 to however many chromosomes you are dealing with. For a human, the total variations are over 8 million. Combining that with the fact of crossing over, means that there are almost an infinite number of genetic variations cause my meiosis.

16. Assessment Statement 10.1.1 Describe the behavior of the chromosomes in the phases of meiosis.

17. The Chiasmata Before the chiasmata can appear, the DNA of one chromatid bonds together with the DNA of a non sister chromatid Then, both the genetic information is transferred from both the father and mother (maternal and paternal chromosomes) this process is called crossing over After the homologous chromosomes are no longer tightly connected, the chiasmata is formed and it links the homologous chromosomes pairs together until late metaphase I

18. Assessment Statement 10.1.4 State Mendel’s law of independent assortment

19. Mendel’s law of Independent Assortment the transmission of traits to the offspring are independent to one another When the chromosomes move to the opposite ends of the pole (of the equator) either chromosome can end up at a specific end However, the movement of one chromosome to a pole does not affect the placement of the other This connects to the law of independent assortment (Mendel’s) because when the homologous chromosome pairs separate, it allows the formation of daughter cells Contributes to Genetic Variation

20. Works Cited "Animation: Random Orientation of Chromosomes During Meiosis." Your Page Title. N.p., n.d. Web. 17 Feb. 2012. <http://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapte r28/animation__random_orientation_of_chro "IB Biology Notes - Meiosis HL." IB Guides - Free International Baccalaureate study guides, notes, videos and powerpoints.. N.p., n.d. Web. 17 Feb. 2012..