1. WHY MEIOSIS? = WHY SEX?
Youtube

2. WHY SEX?
Purifying Selection Hypothesis –
Changing Environment Hypothesis -

3. Why Meiosis? Sea Urchin Sperm and Egg Ascaris lumbricoides
Meiosis = “lessening act”
Ascaris lumbricoides
Body Cells - 4 chromosomes (2n)
Sperm and Egg – 2 chromosomes (n)

4. Chromosomes Come In Distinct Types!
Human Karyotype
Autosomes =
Sex chromosomes =
Homologous chromosomes / homologs =
Allele =
Autosomes ; sex chromosomes; two chromosomes of each type = homologous chromosomes (homologs) = similar in size and shape and carry the same genes; each homologous chromosomes has a version of a gene called an allel

5. Polyploidy

6. Haploid number (n)?
Ploidy?
Total number of chromosomes present?

7. Meiosis is a Reduction Division!
Synapsis; Tetrad; Sister Chromatids; Non-sister chromatids; chiasma(ta)

9. How does sexual reproduction produce offspring that are genetically unique?
1. CROSSING OVER
Synapsis; Tetrad; Sister Chromatids; Non-sister chromatids; chiasma(ta)

10. 2. INDEPENDENT ASSORTMENT OF CHROMOSOMES DURING METAPHASE I
2^n different combinations possible (where n = haploid # of chromosomes) In humans = 2^23= 8.4 million gametes How would genetic variation be affected if maternal chromosomes always had to line up together and paternal chromosomes always had to line up together?

11. How does sexual reproduction produce offspring that are genetically unique?
3. RANDOM FERTILIZATION
You are 1 in…
70,600,000,000,000!!!
Number of different possibilities = product of number of different gametes produced by each parent; In humans = 8.4 million x 8.4 million = 70.6 X10^12 = greater than the total number of people who have ever lived! (does not take into account genetic variation by crossing over)

12. Mistakes in Meiosis
1in 666 infants (0.15 %)

13. Nondisjunction  Aneuploid Cells
Occur frequently; researchers estimate that 25% of all conceptions produce a fertilized egg that is aneuploid  effects are almost severe  lead to spontaneous abortion / miscarriage

14. Nondisjunction Patterns

15. Klinefelter Syndrome
1 in 1000 live male births

16. Triple X
1 in 1000 live births  impaired mental function ; sterility

17. Turner Syndrome
1 in 5000 live births

18. Why no YO syndrome?
Only 86 genes for only a handful of proteins

19. Nondisjunction Patterns
Only 86 genes for only a handful of proteins