Copyright Pearson Prentice Hall 11-4 Meiosis 11-4 Meiosis Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Organisms inherit a single copy of every gene from each of its “parents.” Meiosis separates the two sets of parent genes so that each gamete ends up with just one set. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chromosome Number Chromosome Number All organisms have 2 sets of chromosomes. These two sets of chromosomes are called homologous. These chromosomes are from a fruit fly. Each of the fruit fly’s body cells has 8 chromosomes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chromosome Number A cell that contains both sets of homologous chromosomes is said to be diploid. For Humans, the diploid number is 46, which means we have 23 pairs. The sex cells contain only a single set of chromosomes. These cells are haploid. For Humans, the haploid number is 23. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis Phases of Meiosis Meiosis is a reduction division in which the number of chromosomes per cell is cut in half by separating homologous chromosomes in a diploid cell. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis Meiosis involves two divisions. The diploid cell that entered meiosis will become 4 haploid cells. Copyright Pearson Prentice Hall

Telophase I and Cytokinesis Phases of Meiosis Meiosis I Meiosis I Interphase I During meiosis, the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes. The result of meiosis is 4 haploid cells that are genetically different from one another and from the original cell. Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis Chromosomes & centrioles replicate. Interphase I Interphase I - Cells undergo a round of DNA replication, forming duplicate chromosomes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis Chromosome pairs come together. Crossing over occurs. MEIOSIS I Prophase I MEIOSIS I Prophase I - Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis Crossing-over produces new combinations of genes. Crossing-over occurs during meiosis. (1) Homologous chromosomes form a tetrad. (2) Chromatids cross over one another. (3) The crossed sections of the chromatids are exchanged. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis Chromosome pairs line up on the equator. Each pair attaches to 1 spindle fiber. MEIOSIS I Metaphase I MEIOSIS I Metaphase I - Spindle fibers attach to the chromosomes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis MEIOSIS I Anaphase I The fibers separate the homologous chromosomes and move them toward opposite ends of the cell. MEIOSIS I Anaphase I - The fibers pull the homologous chromosomes toward opposite ends of the cell. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis MEIOSIS I Telophase I and Cytokinesis Nuclear membranes form. The cytoplasm separates into two cells. Meiosis I results in two with half the number of chromosomes as the original cell. MEIOSIS I Telophase I and Cytokinesis - Nuclear membranes form. The cell separates into two cells. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis Meiosis II Neither cell goes through chromosome replication. Each of the chromosomes is still double stranded. The double stranded chromosomes must separate. Copyright Pearson Prentice Hall

Telophase II and Cytokinesis Phases of Meiosis Meiosis II During meiosis, the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes. The result of meiosis is 4 haploid cells that are genetically different from one another and from the original cell. Meiosis II Telophase I and Cytokinesis I Metaphase II Anaphase II Telophase II and Cytokinesis Prophase II Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis MEIOSIS II Prophase II Chromosomes coil. Centrioles move to poles. Spindles form. MEIOSIS II Prophase II - Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis MEIOSIS II Metaphase II The chromosomes line up in the center of cell. MEIOSIS II Metaphase II - The chromosomes line up in a similar way to the metaphase state of mitosis. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis MEIOSIS II Anaphase II The sister chromatids separate and move toward opposite ends of the cell. MEIOSIS II Anaphase II - The sister chromatids separate and move toward opposite ends of the cell. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis MEIOSIS II Telophase II and Cytokinesis Meiosis II results in four haploid daughter cells. MEIOSIS II Telophase II and Cytokinesis - Meiosis II results in four haploid (N) daughter cells. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Gamete Formation Gamete Formation In males meiosis results in four equal-sized sperm. Meiosis produces four genetically different haploid cells. In males, meiosis results in four equal-sized gametes called sperm. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Gamete Formation In females only one egg results from meiosis. The polar bodies die. Meiosis produces four genetically different haploid cells. In females, only one large egg cell results from meiosis. The other three cells, called polar bodies, usually are not involved in reproduction. Copyright Pearson Prentice Hall

Comparing Mitosis and Meiosis Mitosis results in the production of two genetically identical diploid cells. Meiosis produces four genetically different haploid cells. Copyright Pearson Prentice Hall

Comparing Mitosis and Meiosis Cells produced by mitosis have the same number of chromosomes and alleles as the original cell. Mitosis allows an organism to grow and replace cells. Some organisms reproduce asexually by mitosis. Copyright Pearson Prentice Hall

Comparing Mitosis and Meiosis Cells produced by meiosis have half the number of chromosomes as the parent cell. These cells are genetically different from the diploid cell and from each other. Meiosis is how sexually-reproducing organisms produce gametes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 11-4 If the body cells of humans contain 46 chromosomes, a single sperm cell should have 46 chromosomes. 23 chromosomes. 92 chromosomes. between 23 and 46 chromosomes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 11-4 During meiosis, the number of chromosomes per cell is cut in half through the separation of daughter cells. homologous chromosomes. gametes. chromatids. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 11-4 The formation of a tetrad occurs during anaphase I. metaphase II. prophase I. prophase II. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 11-4 In many female animals, meiosis results in the production of only 1 egg. 1 egg and 3 polar bodies. 4 eggs. 1 egg and 2 polar bodies. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 11-4 Compared to egg cells formed during meiosis, daughter cells formed during mitosis are genetically different, while eggs are genetically identical. genetically different, just as egg cells are. genetically identical, just as egg cells are. genetically identical, while egg cells are genetically different. Copyright Pearson Prentice Hall