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I. MEIOSIS INTRO Look Who’s Talking Video Sperm and egg are used to create life. How are sperm and egg created MEIOSIS CHAPTER 10.1 I. MEIOSIS INTRO A. Organisms have tens of thousands of genes B. Genes are not free floating, they are lined up on chromosomes 1. Chromosomes can be about 1000 genes long! II. MEIOSIS VOCAB B. Haploid- When a cell has one kind of chromosome (n) 1. AKA “gamete,” “sex cell,” “sperm” or “egg.” F L Q G F MEIOSIS VOCAB A. Diploid- When a cell has two of each kind of chromosome (2n). 1. Each chromosome has one allele (1 from mom, 1 from dad 2. AKA “Body Cell” F f L Q L q G G F f MEIOSIS VOCAB (CONT.) C. Homologous ChromosomesThe two chromosomes that make up each pair in a diploid cell. F f L Q L q G G F f They aren’t always identical, but they are similar and have the same genes MEIOSIS VOCAB (CONT.) D. Reduction- “Reducing” the number of chromosomes by ½ (haploid) 1. Why? So after fertilization the new organism will have the normal number of chromosomes (diploid) REDUCTION (Making eggs or sperm) Chromosomes Duplicate III. PHASES OF MEIOSIS A. Similar to mitosis (Interphase PMAT- Cytokenesis) B. Goes through PMAT twice 1. 2. 3. 4. Prophase I Metaphase I Anaphase I Telophase I 5. 6. 7. 8. Prophase II Metaphase II Anaphase II Telophase II III. PHASES OF MEIOSIS C. Interphase 1. Cell growth & metabolism 2. Chromosomes duplicate (forms the X) 3. Centrioles duplicate PHASES OF MEIOSIS (cont.) D. Prophase I 1. Chromosomes coil (visible) 2. Nuclear membrane disappears 3. Spindle fibers form PHASES OF MEIOSIS (cont.) D. Prophase I (cont) 3. The duplicated homologous chromosomes pair up to form a tetrad PHASES OF MEIOSIS (cont.) D. Prophase I (cont.) 4. Crossing Over-When homologous chromosomes pair so tightly that they actually exchange pieces of chromatids a. See pg. 267 & 269 PHASES OF MEIOSIS (cont.) 4. Crossing Over (cont.) b. Causes genetic variation c. In humans about 2 crossovers occur in every pair of homologous chromosomes PHASES OF MEIOSIS (cont.) E. Metaphase I 1. The spindle fibers pull the chromosomes to the center 2. The homologous chromosomes stay in tetrads PHASES OF MEIOSIS (cont.) F. Anaphase I 1. The homologous chromosomes are pulled apart to opposite sides 2. This ensures that each new cell will get only 1 chromosome PHASES OF MEIOSIS (cont.) G. Telophase I 1. Nuclear membrane reappears 2. Cytokenis occurs (cell splits) 3. You now have 2 cells (each with 23 chromosome—in humans) PHASES OF MEIOSIS (cont.) G. Meiosis II begins 1. Prophase II, Metaphase II, Anaphase II, Telophase II 2. It looks like mitosis (same # of chromosomes), but there are more cells doing it! PHASES OF MEIOSIS (cont.) H. In the beginning… 1. 1 diploid (2 of each homologous chromosomes) parent cell I. End Result 1. 4 haploid (1/2 the original chromosome number) sex cells (gametes) IV. MITOSIS VS. MEIOSIS MITOSIS MEIOSIS Diploid (2n) Haploid (n) Beginning: 1 cell Beginning: 1 cell End: 2 cells End: 4 cells Identical to parent ½ parent chromes. Dup. Chromos line up alone Dup. Chromos line up in pairs (tetrads) V. NONDISJUNCTION A. Nondisjunction- When homologous chromosomes fail to separate. 1. One gamete will have an extra chromosome (trisomy) 2. One gamete will be missing a chromosome (monosomy) V. NONDISJUNCTION (cont) 3. Trisomy example a. Down syndrome (extra 21st chromosome) 4. Monosomy example a. Turner’s syndrome (missing X chromosome) V. NONDISJUNCTION (cont) B. Polyploidy- Organisms with more than the usual number of chromosomes (3n, 4n, 6n) 1. Plant breeders purposely cause polyploidy to improve their produce a. Bananas (3n), Wheat (6n) VI. VARIATION A. Assortment-The many different ways chromosomes line up during metaphase 1. See picture on 270 B. Genetic Recombination-Major source of gene variation due to reassortment or crossing over. VII. GENE MAPPING A. Crossing over is used to help scientists map the genes on each chromosome 1. The farther apart the two genes are, the more crossing over there will be. VII. GENE MAPPING (cont.) 2. Scientists… 1) Start with one known gene and one unknown gene 2) Find the % of times they cross over 3) Compare that % to other genes on the same chromosome 3. See pg. 272 (Old Books)