11-4 Meiosis 11-4 Meiosis

Where are genes located? On chromosomes in the cell nucleus Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chromosome Number Chromosome Number All organisms have different numbers of chromosomes. A body cell in an adult fruit fly (Drosophila) has 8 chromosomes: 4 from the fruit fly's male parent, and 4 from its female parent. 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 These sets of chromosomes are homologous. Which means each of the 4 chromosomes that came from the male parent has a corresponding chromosome from the female parent. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chromosome Number A cell that contains both sets of homologous chromosomes is said to be diploid = 2 sets. The number of chromosomes in a diploid cell is sometimes represented by the symbol 2N. For Drosophila, the diploid number is 8, which can be written as 2N=8. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Haploid In contrast, gametes (sex cells) of sexually reproducing organisms, including fruit flies contain only a single set of chromosomes and a single set of genes. Haploid = 1 set (or half the number of chromosomes) Can be written as N = 4 N represents the word Haploid Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis Phases of Meiosis 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. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis Meiosis involves two divisions, meiosis I and meiosis II. By the end of meiosis II, the diploid cell that entered meiosis has become 4 haploid cells. Turn to pg. 276 & 277 in the book! Copyright Pearson Prentice Hall

Telophase I and Cytokinesis Phases of Meiosis Prior to Meiosis I, each chromosome is replicated in Interphase I. 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 Cells undergo a round of DNA replication, forming duplicate chromosomes. 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 Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. There are 4 chromatids in a tetrad. 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 As homologous chromosomes pair up & form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing over. Crossing-over produces new combinations of alleles (the different forms of a gene). 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 Metaphase, Anaphase, Telophase, and Cytokinesis all resemble the patterns of mitosis. Metaphase- Middle Anaphase- Away Telophase & Cytokinesis- Two Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Phases of Meiosis Meiosis II The two cells produced by meiosis I now enter a second meiotic division. Unlike meiosis I, neither cell goes through Interphase again. Each of the cell’s chromosomes now have 2 chromatids instead of 4. 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 Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell. 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 (N) 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 male animals, meiosis results in four equal-sized gametes called 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 many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction. 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 A diploid cell that divides by mitosis gives rise to 2 diploid (2N) daughter cells. The daughter cells have: chromosomes and alleles identical to one another and to the original cell. Allows an organism’s body to grow and replace cells. In ASEXUAL REPRODUCTION, a new organism is produced by mitosis of the cell or cells of the parent organism. Copyright Pearson Prentice Hall

Comparing Mitosis and Meiosis Begins with a diploid cell but produces 4 haploid (N) cells. The new cells are genetically different from the diploid cell and from one another. This is how SEXUALLY reproducing organisms produce gametes Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Did Mrs. Dayton and Mr. Dayton’s cells go through mitosis or meiosis? Copyright Pearson Prentice Hall

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

END OF SECTION