2. MEIOSIS Required for sexual reproduction Greatest advantage of sexual reproduction: GENETIC VARIABILITY (genetic differences) Why are genetic differences good??

3. WHY ARE GENETIC DIFFERENCES GOOD? Superb specimens Lance Armstrong Heart pumps more blood/minute High lung efficiency Muscles produce less lactic acid, more efficient at removing lactic acid Inferior specimens Person with sickle cell anemia RBC – sickle shaped, cannot carry O 2 as efficiently Strenuous exercise must be avoided Pain crisis Death can occur

4. WHAT CONTRIBUTES TO GENETIC VARIABILITY?

5. #1 INDEPENDENT ASSORTMENT Random “sorting” of chromosomes To show this: Spermatogenesis Oogenesis (Gametogenesis)

6. SPERMATOGENESIS 4 genetically different haploid cells

7. OOGENESIS

8. FORMULA FOR # OF DIFFERENT GAMETES YOU CAN PRODUCE 2 n, n= haploid # Example: 2 2 = 4 genetically different gametes Humans- n = 23 2 23 = 8,000,000 genetically different sperm = 8,000,000 genetically different eggs

9. #2 CROSSING OVER Exchange of genetic material from 2 homologous chromosomes Occurs during Prophase I

10. #3 RANDOM FERTILIZATION What sperm reaches / fertilizes the egg is a random event 1/8,000,000 possible eggs 1/8,000,000 possible sperm