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Transcript
1 10.4—Meiosis I. Chromosome number A. Homologous chromosomes 1. Chromosomes that each have a corresponding chromosome from the opposite sex parent 2. Humans have a 23 pairs of homologous chromosomes a. 23 from mother b. 23 from father c. For a total of 46 B. Diploid Cells 1. Means “two sets” 2. Diploid cells contain: a. Two complete sets of chromosomes b. Two complete sets of genes 3. Humans have 46 homologous chromosomes, and therefore a diploid number of 46 a. 2N = 46 C. Haploid Cells 1. Cells contain a SINGLE set of chromosomes 2. In sexually reproducing organisms a. Gametes or sex cells are haploid 2 b. Contain ½ the number of chromosomes found in the diploid parent c. Example: Human i. 2N = 46 ii. Egg and sperm cells are the gametes Each has a N = 23 II. Phases of Meiosis A. Meiosis is… 1. Process of reduction division of a diploid cell in which the number of chromosomes per cell is cut in half during the separation of homologous chromosomes 2. Results in the production of 4 haploid cells (gametes) B. Consists of two phases 1. Meiosis I 2. Meiosis II Meiosis I Interphase I DNA replicates Chromosomes are replicated Cell prepares for meiosis 3 **Prophase I ** Chromosomes pair with its corresponding homologous chromosome o This is called a TETRAD Crossing-over occurs here o Portions of the chromatids in the tetrad EXCHANGE genetic material o One of the main reasons why life is genetically diverse! Metaphase I Chromosomes line up on the metaphase plate Tetrad attaches to the spindle fibers at the centromere Anaphase I Spindle fibers pull homologous chromosomes to opposite ends of the cell Telophase I and Cytokinesis Nuclear membrane reforms Cytoplasm pinches off and 2 haploid daughter cells are formed 4 Meiosis II Prophase II Chromosomes become visible Spindle forms Metaphase II Chromosomes line up in the metaphase plate Attach to spindle fibers Anaphase II Spindle fibers pull chromatids to opposite ends of the cell Telophase II and Cytokinesis Nuclear membrane reforms Cytoplasm is pinched off 4 genetically unique haploid daughter cells are formed 5 III. Meiosis vs, Meiosis Mitosis 2N or N Type of cell at the beginning 1 Number of phases 2 identical cells Result Meiosis 2N 2 4 genetically different haploid cells Used for: Grow and replace cells Production of gametes Asexual reproduction Sexual reproduction IV. Gene Linkage A. Some genes are linked together and therefore, inherited together B. These linked genes are called linkage groups 1. Linkage groups are found on the same chromosome V. Gene Maps A. 1911—Alfred Sturtevant 1. Found the farther apart the gene the more likely crossing over will occur 2. Gene map a. Shows the relative location of genes on a chromosome b. Used to identify specific genes on a chromosome c. Human genome