1. Meiosis
Chapter 10, Section 2

2. Diploid & Haploid Cells
Diploid = a cell with two sets of chromosomes, 2n, somatic (body) cells
muscle, skin, liver, etc.
Haploid = a cell with one set of chromosomes, gametes, 1n, sperm and eggs
Meiosis forms haploid gametes required for sexual reproduction
Meiosis has 2 stages
Meiosis I
Meiosis II

3. Interphase and stages of mitosis

4. Chromosomes from metaphase stage of mitosis

5. Below are chromosomes after they split into chromatids during (telophase) of mitosis

6. Separation of homologous pairs
 MEIOSIS I
Separation of homologous pairs
Homologous Pair = in a diploid cell the 2 sets of chromosomes pair up

7.  1. Prophase I DNA coils into chromosomes
Nuclear envelope & nucleolus break down
Synapsis = homologous chromosomes pair up into tetrads
Crossing-over = homologous pairs switch pieces of their chromatids
Genetic Recombination = maternal & paternal genetic info get shuffled during crossing-over

9.  2. Metaphase I Tetrads line up in the middle of the cell
Spindle fibers attach at the centromeres of each homologous chromosome

11.  3. Anaphase I
Each homologous chromosome moves to the opposite end of the cell
Independent Assortment = random separation of chromosomes, allows for genetic variation

13.  4. Telophase I & Cytokinesis I
Two newly formed cells are haploid
Each chromosome is still made up of two chromatids

15. Separation of sister chromatids
 MEIOSIS II
Separation of sister chromatids
Sister Chromatids = identical halves of a chromosome that has been duplicated

16.  5. Prophase II
2 newly created cells from Meiosis I start to divide

17.  6. Metaphase II
Chromosomes line up in the center

18.  7. Anaphase II
Sister Chromatids separate

19.  8. Telophase II & Cytokinesis II
4 new cells, each with half the number of chromosomes of the original cell

20. Development of Gametes
Spermatogenesis = production of sperm cells
Oogenesis = production of mature egg cells

21. Nondisjunction
Nondisjunction = failure of homologous pairs to separate in Meiosis I
If an organism survives, it may have a genetic disorder

22. Polyploidy
Polyploid = organisms with more than the usual number of chromosome sets
Occurs frequently in plants, results in plants that are larger than normal