1. MEIOSIS AND PRODUCTION OF GAMETES Mr. Taylor Biology Rainier High School

2. Meiosis and Gamete Production Meiosis is the process of creating new cells (called gametes) by performing two separate cell divisions. Meiosis is the process of creating new cells (called gametes) by performing two separate cell divisions. Process closely resembles mitosis, shares similar names with mitosis. Process closely resembles mitosis, shares similar names with mitosis. Begins with chromosomes replicating in late Interphase. Begins with chromosomes replicating in late Interphase.

3. Meiosis and Gamete Production PROPHASE I PROPHASE I –Chromosomes have replicated, now coil into tight rods –Nuclear membrane breaks down –Spindle begins to form  Homologous chromosomes pair up.  This forms a structure called a TETRAD.

4. Meiosis and Gamete Production METAPHASE I METAPHASE I –Homologous pairs (tetrads) align along the equator (middle) of the cell. ANAPHASE I ANAPHASE I –Centromeres DO NOT divide, chromatids DO NOT separate. –Homologous chromosome pairs go to opposite poles. –This is called the REDUCTION DIVISION. The resulting cells will be haploid as they only have one set of chromosomes.

5. Meiosis and Gamete Production

6. TELOPHASE I TELOPHASE I –Nucleus reforms, chromosomes begin to uncoil –Cytokinesis occurs, cell membrane connects to form 2 new cells. –These new cells are HAPLOID. They contain pairs of chromosomes, but only ONE set. No chromosome has its homologous partner present. NOW OCCURS ONE BIG DIFFERENCE BETWEEN MITOSIS AND MEIOSIS… NOW OCCURS ONE BIG DIFFERENCE BETWEEN MITOSIS AND MEIOSIS…

7. Meiosis and Gamete Production THERE IS NO INTERPHASE BETWEEN MEIOSIS I AND MEIOSIS II. –T–T–T–This means that the chromosomes DO NOT REPLICATE again. The cells go directly from Telophase I into … PROPHASE II –N–N–N–Nuclear membranes dissolve again. –N–N–N–New spindles form, centromeres attach –C–C–C–Chromosomes coil tightly again.

8. METAPHASE II METAPHASE II –Chromatids align along the equator (middle) of the cell ANAPHASE II ANAPHASE II –Centromeres divide. –Chromosomes are pulled to opposite poles of the cells by the spindle fibers.

9. Meiosis and Gamete Production TELOPHASE II TELOPHASE II –Nuclear membranes reform. –Chromosomes uncoil. –Spindles break down. –Cytokinesis occurs… Cell membranes divide cells (now have 4 cells).

10. Meiosis and Gamete Production Meiosis I Prophase IMetaphase I Anaphase ITelophase I

11. Meiosis and Gamete Production Meiosis II Prophase IIMetaphase IIAnaphase II Telophase II

12. Meiosis and Gamete Production CROSSING OVER During Prophase I while the homologous sister chromatids are sitting tightly against each other as a tetrad, small portions of “identical” chromatids can swap places. The end result is that a chromatid from “mom” has a section of a chromatid from “dad” (and vice versa). This greatly increases the genetic variation possible…and the whole reason for sexual reproduction is to create individuals that are different from each other.

13. Meiosis and Gamete Production LAW OF INDEPENDENT ASSORTMENT Each chromosome of each homologous pair will be pulled toward the poles of the new cells independently. This results different mixtures of chromosomes in the gametes.

14. Meiosis and Gamete Production LAW OF INDEPENDENT ASSORTMENT Each chromosome of each homologous pair will be pulled toward the poles of the new cells independently. This results different mixtures of chromosomes in the gametes.

15. Meiosis and Gamete Production By this method of independent assortment: 2 chromosomes make 1 pair and will yield 2 combinations AA pairs to A and A 4 chromosomes make 2 pair and will yield 4 combinations A A B B pairs AB, A B, A B, A B 6 chromosomes make 3 pair and will yield 8 combinations A A B B C C pairs ABC, AB C, A B C, A BC, A BC, A B C, A B C, A BC

16. By this method of independent assortment: 8 chromosomes make 4 pair and will yield 16 combinations AaBbCcDd pair ABCD, ABCd, ABcD, ABcd, AbCD, AbCd, AbcD, Abcd, aBCD, aBCd, aBcD, aBcd, abCD, abCd, abcD, abcd 46 chromosomes make 23 pair and will yield 2 23 or 8,388,608 combinations and this is not including crossing over!!

17. Spermatogenesis The process of forming male gametes / spermatozoa One spermatogonia leaving Interphase I will produce 4 sperm DIPLOID HAPLOID **>>**>> ** ** >> >> ** >> ** >> *>

18. Meiosis and Gamete Production Oogenesis The process of forming female gametes / ova One oogonia will produce only one ovum. The three polar bodies will not mature and will be reabsorbed by the female’s body. DIPLOID HAPLOID **>>**>> ** ** >> >> ** >> ** >> *>*> *>*>*>*> *>*> *>*>

19. Thank you for your attention. Thank you for your attention. You may now complain to your teacher about writer’s cramp. It probably won’t do any good, but you can complain. You may now complain to your teacher about writer’s cramp. It probably won’t do any good, but you can complain.