11-4 Meiosis I. Chromosome Number A. Homologous- corresponding chromosomes, one from the male and one from the female. B. Diploid - A cell that contains both sets of homologous chromosomes. 2N C. Haploid - a cell that contains only a single set of genes. N

11-4 Meiosis II. Phases of Meiosis A. Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. A. Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.

11-4 Meiosis A. Meiosis I- 1. Prior to meiosis I the chromosomes replicate. 2. Interphase I- Cells undergo a round of DNA replication, forming duplicate chromosomes.

11-4 Meiosis 3. In Prophase of meiosis I each chromosome pairs with its corresponding homologous chromosome to form a structure called a tetrad. There are four chromatids in a tetrad. As the homologous chromosomes line up they exchange portions of their chromatids in a process called crossing over. The exchange produces new forms of the alleles.

Crossing Over

11-4 Meiosis 4. Metaphase I- Spindle fibers attach to the chromosomes. 5. Anaphase I- The fibers pull the chromosomes toward the opposite ends of the cell.

11-4 Meiosis 6. Telophase and Cytokinesis- Nuclear membrane form. The cell separates into two cells. 7. At the end of Meiosis I there are two cells formed. But, unlike mitosis each daughter cell has a set of chromosomes that is unique to that cell. The alleles have been shuffled like a deck of cards.

Meiosis I

11-4 Meiosis B. Meiosis II 1. Prophase II- Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell. 2. During metaphase II of meiosis, chromosomes line up at the center of each cell.

11-4 Meiosis 3. In anaphase II the paired chromatids separate and move towards opposite ends of the poles. 4. Telophase II and Cytokinesis- Each of the four daughter cells produced only contain the haploid number (N).

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase IIMetaphase IIAnaphase IITelophase II The chromosomes line up in a similar way to the metaphase stage of mitosis. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells. Meiosis II

11-4 Meiosis C. Gamete Formation 1. In males the haploid gametes that are formed are called sperm. 2. In females generally only one of the cells produced forms an egg, and the other three form polar bodies.

Spermatogenesis

OOGENESIS

11-4 Meiosis III. Comparing Mitosis and Meiosis A. Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid cells. A. Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid cells.