1. Meiosis

2. I. Reproduction A. Asexual: 1. simple cell division
2. two new genetically identical cells
3. offspring inherit all genetic info from one
parent
4. usually single celled (protists, bacteria)
5. some multi-cellular (plants, starfish)

3. B. Sexual:
1. genetic mat’l from both parents combine
2. offspring differ from each parent
3. union of sex cells
4. Genetic variation

4. C. Meiosis:
1. Reduction Division
2. Formation of gametes (egg and sperm)
3. Ploidy: number of sets of chromosomes
a) diploid (2n)
-2 sets of chromosomes
- humans  46
b) haploid(1n)
- 1 set of chromosomes
- gametes
- humans  23

5. 4. 4 daughter cells
a) Start with 1 diploid  end with 4 haploid cells
b) Humans 46  (23, 23, 23, 23)
5. Two stages:
a) Meiosis I (prophase I, metaphase I, anaphase I, & telophase I)
b) Meiosis II (metaphase II,
anaphase II, & telophase II)

6. 6. Genetic Variation:
a. Gamete possible combinations = 2n
where: n = number sets of chromosomes
b. Ex:
i. n = 2 : 22 = 4 gamete poss
ii. Humans n = 23: 223 = ~8 million!!!
AaBb
AB Ab aB ab

7. c. Crossing Over
1. Tetrads: homologous
chromosomes stick together
gene – by –gene
2. exchange of genetic
material (genetic recombination)

10. 7. Significance A. Formation of the gametes
B. 4 haploid daughter cells
C. Crossing over provides genetic
variation (Prophase I)

11. Mitosis vs Meiosis