3. Plants have multicellular haploid stage.

4. Grasshopper chromosomes (color added)

7. Simplification shows cell with diploid 2N=2.

10. In this example 2N=4; the “long” pair and the “short”.

12. Remember mitosis? Cells produce more identical cells. Resembles Meiosis II, when sister chromatids separate and cells divide.

13. Meiosis I is reduction division when diploid --> haploid. Meiosis II is similar to mitosis; doubles cell number.

14. Watch meiosis video,if possible.

15. How does meiosis generate variation?

17. Even without crossing over, meiosis generates variation. 2 N combinations of maternal and paternal chromosomes. Humans: 2 23 = 8.4 million Recombination dramatically increases possibilities. In humans, about 50 chiasmata in meiosis I. Almost limitless variety of re-shuffling.

18. Recombination scrambles chromosomes. Figure from Hapmap.com

19. Black Oxford Canadian Strawberry Goldrush 4 of the 79 apple varieties sold at Fedco seeds in Albion ME Liberty

20. Sex is costly.

21. Abundance of trematode parasites Predominance of sex in snail hosts Sexuality important in escaping parasites.

22. Errors in meiosis