1. Unit 4 – Lecture 2

2. Discuss Review the stages of Mitosis [cell cycle] with your partner. Mitosis – cell division in somatic [body] cells [I]PMAT [interphase] prophase metaphase anaphase telophase

3. Meiosis Meiosis – cell division to create gametes sex cells / reproductive cells / egg&sperm Meiosis I – IPMAT Meiosis II – PMAT

4. Meiosis I Meiosis I – similar to mitosis [diff in red] [interphase…] Prophase I chromosomes condense nuclear envelope disappears homologous chromosomes pair instead of chromatids crossing over occurs

5. Crossing Over Crossing over – exchange of genetic information between homologous chromosomes contributes to genetic diversity of resulting gametes homologous chromosome pair = tetrad tetra = four not required: chiasma(ta) – place at which crossing over occurs

6. Meiosis I – cont’d [Meiosis I] Metaphase I spindle fibers move tetrads to cell equator [similar to metaphase plate / equatorial plate in mitosis]

7. Meiosis I – cont’d [Meiosis I] Anaphase I homologous chromosomes are each pulled by spindle fibers to cell poles

8. Meiosis I – cont’d [Meiosis I] Telophase I homologous chromosomes each arrive at cell poles nuclear envelopes reform spindle fibers break down cytoplasm divides [cytokinesis]

9. Meiosis I – cont’d Meiosis I: End Result – 2 diploid cells with: same amount of information different combination of information

10. Meiosis II Meiosis II – process is just like mitosis NO SECOND INTERPHASE. [PMAT]

11. Discuss What processes happen during interphase? If there is no interphase, what processes are NOT going to happen in between the first stages of meiosis and the second meiosis?

12. Meiosis II – cont’d [Meiosis II] Prophase II spindle fibers form nuclear envelopes dissolve

13. Meiosis II – cont’d [Meiosis II] Metaphase II – chromosomes line up at equator

14. Meiosis II – cont’d [Meiosis II] Anaphase II chromosomes pulled apart at centromeres; [form chromatids] chromosomes [chromatids] pull toward poles

15. Meiosis II – cont’d [Meiosis II] Telophase II – nuclear envelopes reform spindle fibers break down cytokinesis

16. Meiosis II – cont’d Meiosis II: End Result – 4 haploid cells with: half of info as original cell different combination of information

17. Meiosis – cont’d Cells produced from meiosis are genetically different due to: crossing over [in prophase I] independent assortment [in metaphase I] random distribution of homologues in metaphase I

19. Meiosis – cont’d More than 8 million [ 2 23 ] combinations of genes in humans PER PARENT [w/ only IA] total…with 2 parents combining genes… = >70 trillion combinations [ 2 23 * 2 23 ]