1. Two types of Cell Division Mitosis and Meiosis

2. What is the purpose of cell division? Growth Repair Replace Reproduce

3. Two types of Reproduction Asexual by mitosis One parent Offspring identical to parent Advantages? Disadvantages? Examples in: Prokaryotes Protist/Fungi Plants Sponges etc

4. Sexual Reproduction Process by which two cells (egg and sperm) - from two parents join together to form one cell (zygote) which then develops into the offspring Advantage Variation Disadvantage Look for mates, loss of gametes, (energy investment) Chromosome number incompatibility!

5. Chromosome numbers: All eukaryotic cells have pairs of chromosomes where one of each pair are form each parent. Haploid (N) = Half the number of chromosomes in an eukaryotic cell. Usually one of each pair Diploid (2N) = total of number chromosomes in an eukaryotic cell.

6. Homologous Chromosomes ID of Paired chromosomes (homologous) Centromere position Similar size Similar genes or alleles in the same locus Stain the same p.138ap.138a

8. What needs to happen before fertilization? Meiosis: The egg/sperm cell will have N chromosomes (or one of each pair). Fertilization: When egg and sperm unite – parental chromosome number is restored (N + N  2N) How is meiosis different from mitosis?

9. multicelled body meiosis diploid fertilization zygote gametes haploid Fig. 9-8b, p.146

10. Overview of Meiosis Overview of Meiosis

11. Prophase I Common to mitosis Nuclear membrane disappears Centrioles divide and migrate to poles Spindle fibers form Different Synapsis (homologous chromosomes come together Called Tetrads Crossing over

12. Crossing Over Segments between homologous chromosome are exchanged (swapped) Results in new combinations of genes

13. plasma membrane newly forming microtubules in the cytoplasm spindle equator (midway between the two poles) one pair of homologous chromosomes PROPHASE IMETAPHASE IANAPHASE ITELOPHASE I MEIOSIS I Fig. 9-5a, p.142

14. Metaphase I Tetrads line up on the equator Anaphase I Homologous chromosomes separate and go to the poles Telophase I Chromosomes may become diffuse and nuclear membrane forms Cytokinesis I 2 cells formed Meiosis I cont….

15. plasma membrane newly forming microtubules in the cytoplasm spindle equator (midway between the two poles) one pair of homologous chromosomes PROPHASE IMETAPHASE IANAPHASE ITELOPHASE I MEIOSIS I Fig. 9-5a, p.142

16. no interphase between nuclear divisions TELOPHASEPROPHASEANAPHASEMETAPHASETELOPHASE IIPROPHASE IIANAPHASE IIMETAPHASE II typically two nuclei ( n ) Crossing over occurs between homologues. Homologues separate from their partner. Homologous pairs align randomly. four nuclei ( 4n ) Sister chromatids of chromo-somes seperate. Chromosomes align at spindle equator. Fig. 9-11b, p.148

17. Meiosis II Prophase II: Chromosomes condense – have the X shape Metaphase II: Chromosomes line up on the equator Anaphase II: Centromeres split and chromosomes migrate to the poles Telophase II: Two nucleii form (cell plate or cleavage furrow forms) Cytokinesis: Two new cells form – each containing _____ chromosomes

18. a Growthb Meiosis I and cytoplasmic division c Meiosis II and cytoplasmic division ovum (haploid) primary oocyte (diploid) oogonium (diploid female reproductive cell) secondary oocyte (haploid) first polar body (haploid) three polar bodies (haploid) Fig. 9-10a, p.147

19. a Growth b Meiosis I and cytoplasmic division c Meiosis II and cytoplasmic division cell differentiation, sperm formation (mature, haploid male gametes) spermatids (haploid) secondary spermatocytes (haploid) primary spermatocyte (diploid) spermato- gonium (diploid male reproductive cell) Fig. 9-9, p.147

20. How does meiosis produce variation? 1. Crossing over between homologous chromosomes 2. Independent assortment of different chromosomes during Metaphase I 2 23 = 8,388,608 combinations! 3. Random Fertilization of gametes

21. Chromosomal Abnormalities Nondisjunction of homologous chromosomes Downs, Klinefelters, Turners Syndrome Chromosomal breakage during crossing over that results in segments of chromosomes showing Deletion Inversion Translocation Duplication