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BELLWORK: 1. Mitosis occurs in what type of cells in our body? ______________ cells 2. Meiosis occurs only in our ________________ http://www.youtube.com/watch?v=hVUKoEFYClo B ELLWORK : Draw and write the name of each numbered item: 1. _______________ 2. _______________ 3. _______________ 4. _______________ 5. _______________ 6. What phase of mitosis is this cell in?_____________ BELLWORK: Thurs. OCT. 29, 2015 Cell are limited in size by ____________ and ______________ 2. _________ cells can become any type of cell 3. _________________ hold sister chromatids together. 4. A chromosome consists of 2 identical sister _____________________ 1. WHY DO CELLS DIVIDE (“DO MITOSIS”…) One-celled organisms: for reproduction asexual reproduction (clones) amoeba Multi-celled organisms for growth and development from fertilized egg to adult for repair and replacement replace cells that die from normal wear & tear or from injury starfish GETTING FROM THERE TO HERE… Going from egg to baby…. the original fertilized egg has to divide… and divide… and divide… and divide… But how did it all start??? But how did the egg cell and the sperm cell end up with half each (23) the normal human number of chromosomes (46) … so you didn’t have too many? 11.4 MEIOSIS 11-4 MEIOSIS meiosis Chromosomes: strands of DNA and protein inside the cell nucleus are the carriers of genes. Genes: are located in specific positions on chromosomes. An organism must inherit a single copy of every gene from each of its “parents.” Copyright Pearson Prentice Hall So…Gametes are formed by a process that separates the two sets of genes so that each gamete ends up with just one set. This makes the sperm cell and the egg cell… Gametes when the two sets of genes in an organism are separated into one set. The male gamete in animals is the: Sperm!!! In higher plants it is: Pollen!!!! The female gamete in animals is the: Egg or Ova!!! In higher plants it is: Seed or ovule!!!! Chromosome Number All organisms have different numbers of chromosomes. Diploid: cell that contains both sets of homologous chromosomes. The number of chromosomes in a diploid cell = 2N. For Drosophila (fruit flies), the diploid number is 8 Or 2N=8. A body cell of a human has 46 chromosomes and are DIPLOID. 2N = 46 COMING UP: Our gametes (egg/sperm) have 23 chromosomes and are HAPLOID N = 23 Copyright Pearson Prentice Hall All of our body cells are Diploid and have 46 chromosomes in their nuclei: Haploid cells: contain only a single set of chromosomes, and a single set of genes. Gametes of sexually reproducing organisms are haploid. Remember: Haploid = Half the chromosome number Haploid cells are represented by the symbol N. For Drosophila (fruit flies) the haploid number is 4, which can be written as N=4. Our gametes (egg/sperm) have 23 chromosomes and are HAPLOID N = 23 REMEMBER: A body cell of a human has 46 chromosomes and are DIPLOID. 2N = 46 GAMETES Think of sperm and eggs as half cells 23 23 HALF “PLOID” • A body cell in an adult fruit fly has 8 chromosomes: 4 from the fruit fly's male parent, and 4 from its female parent. These sets of chromosomes are homologous. Each of the 4 chromosomes that came from the male parent has a corresponding chromosome from the female parent. Meiosis is a reduction division. The number of chromosomes per cell is cut in half as homologous chromosomes separate from a diploid cell. Meiosis involves 2 divisions, meiosis I (PMAT1) & meiosis II (PMAT2) By the end of meiosis II, the diploid cell that entered meiosis has become 4 haploid cells. Meiosis I Interphase I Meiosis I Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Cells undergo a round of DNA replication, forming duplicate chromosomes. Interphase I Crossing over: when homologous chromosomes form tetrads and exchange portions of their chromatids in MEIOSIS 1 THIS produces new combinations of alleles – genes which is why we don’t all look alike!!!!! from mom from dad from mom from dad from mom from dad Tetrad: when chromosomes pair with their homologous chromosome There are 4 chromatids in a tetrad. MEIOSIS I Prophase I Spindle fibers attach to the chromosomes. MEIOSIS I Metaphase I Centrioles The fibers pull the homologous chromosomes toward opposite ends of the cell. MEIOSIS I Anaphase I Nuclear membranes form. The cell separates into 2 cells with chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I. MEIOSIS I Telophase I and Cytokinesis Meiosis II The 2 cells made by meiosis I enter a 2nd meiotic division. Unlike meiosis I, neither cell goes through chromosome replication. Each of the cell’s chromosomes has 2 chromatids. Meiosis II Telophase I and Cytokinesis I Meiosis II Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell. MEIOSIS II: Prophase II Phases of Meiosis The chromosomes “meet” orline up in the center of cell. MEIOSIS II: Metaphase II Phases of Meiosis The sister chromatids separate and move toward opposite ends of the cell. MEIOSIS II Anaphase II Copyright Pearson Prentice Hall Meiosis II results in four haploid (N) daughter cells. MEIOSIS II Telophase II and Cytokinesis Gamete Formation In male animals, meiosis results in four equal-sized gametes called sperm. In many female animals, one egg results from meiosis. The other three cells are tiny polar bodies which basically shrivel up an die The egg gets most of the cytoplasm Comparing Mitosis and Meiosis Mitosis results in the production of two genetically identical diploid cells. Meiosis produces four genetically different haploid cells. • meiosis=related • This starts on page 323 • Due Tuesday but start working NOW BELLWORK: FRI. NOV. 12, 2010 1. Meiosis occurs in _____ cells (__________), produces ___ genetically ____________ cells. 2. Mitosis occurs in _________ cells, produces ___ genetically ____________ cells. • http://www.pearsonsuccessnet.com/snpap p/iText/products/0-13-1811185/ch11/ch11_s4_1.html Comparing Mitosis and Meiosis Mitosis • 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 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 11-4 Copyright Pearson Prentice Hall 11-4 If the body cells of humans contain 46 chromosomes, a single sperm cell should have a. 46 chromosomes. b. 23 chromosomes. c. 92 chromosomes. d. between 23 and 46 chromosomes. Copyright Pearson Prentice Hall 11-4 During meiosis, the number of chromosomes per cell is cut in half through the separation of a. daughter cells. b. homologous chromosomes. c. gametes. d. chromatids. Copyright Pearson Prentice Hall 11-4 The formation of a tetrad occurs during a. anaphase I. b. metaphase II. c. prophase I. d. prophase II. Copyright Pearson Prentice Hall 11-4 In many female animals, meiosis results in the production of a. only 1 egg. b. 1 egg and 3 polar bodies. c. 4 eggs. d. 1 egg and 2 polar bodies. Copyright Pearson Prentice Hall 11-4 Compared to egg cells formed during meiosis, daughter cells formed during mitosis are a. genetically different, while eggs are genetically identical. b. genetically different, just as egg cells are. c. genetically identical, just as egg cells are. d. genetically identical, while egg cells are genetically different. Copyright Pearson Prentice Hall