Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Meiosis and Gametes 1Chapter 11 Sexual Reproduction and MeiosisRev QuestionMeiosis and Gametes 2When and where does meiosis occur in humans?Why is meiosis necessary?“reductive division”Meiosis and Gametes 3What are the stages of Meiosis?Meiosis I vs Meiosis IIProphase IMetaphase IAnaphase ITelophase IMcGraw-Hill MeiosisMeiosis unique featuresMeiosis and Gametes 4How does Prophase I differ from Prophase of Mitosis?1) Bivalents form -- “synapsis”-- homologous chromosome pairs2) Crossing over occurs-- exchange of DNA segments-- “chiasmata”During Metaphase 1,bivalents are aligned at equatornot individual chromosomes QuestionMeiosis and Gametes 5During Meiosis I parental homologous chromosomes are independently sorted to daughter cellsChromosome reduction occurs during Meiosis IInterkinesisWhat happens during Meiosis II?Chromosome reduction ---- sister chromatids separateGametes producedMcGraw-Hill sorting QuestionMeiosis and Gametes 6Comparison of Meiosis and MitosisMetaphase looks differentfor each process2N=4QuestionQuestionMeiosis and Gametes 7Homework assignment:10 points: due next classFor a cell where 2N=6, draw a series of diagrams showing the chromosomes moving through the stages of meiosis.In one of the diagram clearly label:-- a pair of homologous chromosomes-- a bivalentLabel all stagesMake diagrams large, clear and neatAlso answer the following questions:For an organism with a chromosome number of 2n = 56:A. How many pairs of homologous chromosomes does each normal body cell possess? ___B. How many chromosomes does each cell possess after mitosis? ____C. How many pairs of sister chromatids are present at the beginning of meiosis? ___D. How many bivalents will form during prophase-I? ____E. How many chromosomes does each cell possess after meiosis? ___Drawings must be neatly done and chromosomes drawn with adequate detail. Chromosomes, bivalents and spindle fibers must be recognizable as these structures.Meiosis and Gametes 8Why does meiosis in females yieldonly 1 viable gamete?Why does spermatogenesis in males assure 50:50 ratio of males to females?Sex of the sperm determines sex of the offspringMeiosis and Gametes 9How can errors during meiosis causeCongenital birth disorders?Non-disjunction of chromosomese.g., Down’s syndromeWhat is karyotyping?“trisomy 21”-- an example of “aneuploidy”Many effects-- reduced intellectual development-- heart and kidney defects-- often fatal-- early onset Alzheimer'sMeiosis and Gametes 10How does meiosis create genetic diversity?1) crossing over2) random assortment of chromosomesand later …3) random pairing of