Meiosis Chapter 10.1 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

2. Formation of gametes= Fertilization(egg and sperm) C. Meiosis: 1. Reduction Division 2. Formation of gametes= Fertilization(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 Reduction division – reduces the number of chromosomes Somatic cells are diploid, gametes are haploid

a) Start with 1 diploid  end with 4 haploid cells 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) Phases in meiosis are generally the same as in mitosis but occur twice (Meiosis I and 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

chromosomes stick together gene – by –gene 2. exchange of genetic c. Crossing Over 1. Tetrads: homologous chromosomes stick together gene – by –gene 2. exchange of genetic material (genetic recombination) -chromosomal segments are exchanged Homologous chromosomes are two sister chromatids, one from the father and one from the mother, containing the same general genetic information (causes genetic variation)(Occurs in Prophase I) Crossing over or genetic recombination may occur when DNA from one chromosome switches places with the same material on the homolgous chromosome

During Meiosis I, homologous chromosomes are separated During Meiosis II, Sister chromatids are separated

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

Mitosis vs Meiosis