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

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

WHAT CONTRIBUTES TO GENETIC VARIABILITY?

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

SPERMATOGENESIS 4 genetically different haploid cells

OOGENESIS

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

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

#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