Meiosis http://www.estrellamountain.edu/faculty/farabee/biobk/BioBookmeiosis.html

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)

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

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

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. 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

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

http://www.accessexcellence.org/RC/VL/GG/images/meiosis.gif

http://genetics.gsk.com/graphics/meiosis-big.gif

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

Mitosis vs Meiosis http://post.queensu.ca/~forsdyke/images/darwin04.gif