Chapter 12 Meiosis and Alteration of Generations PDF

Because learning changes everything. ® Chapter 12 Meiosis and Alternation of Generations FIFTEENTH EDITION James E. Bidlack, Shelly H. Jansky © 2021 McGraw Hill. All rights reserved. Authorized only for instructor use in the classroom. No reproduct...

Because learning changes everything. ® Chapter 12 Meiosis and Alternation of Generations FIFTEENTH EDITION James E. Bidlack, Shelly H. Jansky © 2021 McGraw Hill. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill.  Outline Introduction to Meiosis and Alternation of Generations The Phases of Meiosis Division I (Meiosis l, or Reduction Division) Division II (Meiosis ll, or Equational Division) Alteration of Generations © McGraw Hill © Image Source/Getty Images 2  Introduction to Meiosis and Alternation of Generations Asexual reproduction - Production of cells identical in chromosomes with cells from which they arose Sexual reproduction - In nearly all plants Results in formation of seeds in flowering and cone- bearing plants Gametes produced. Egg and sperm unite to form zygote. © McGraw Hill 3  Asexual and Sexual Reproduction Access the text alternative for slide images. © McGraw Hill © Shelley H. Jansky 4  A Comparisonof Mitosis and Meiosis Access the text alternative for slide images. © McGraw Hill 5  Mitosis and Meiosis Access the text alternative for slide images. © McGraw Hill 6  Chromosomes and Meiosis Cells have two sets of chromosomes, one set from each parent. Members of each pair of chromosomes are identical in: Length Amount of DNA Genes carried Location of centromere Homologous chromosomes = chromosome pairs Results of meiosis: Four cells from two successive divisions Cells with half the chromosome number of parents Each cell rarely identical to original cell or each other. © McGraw Hill 7  The Phases of Meiosis Before meiosis, DNA molecules of each chromosome double. Each chromosome has identical DNA molecules held together by a centromere. Meiosis: Division I (Meiosis I or Reduction Division) - Number of chromosomes reduced to half. Division II (Meiosis II or Equational Division) - No further reduction in chromosome number. © McGraw Hill 8  The Phases of Meiosis Division I Prophase I Chromosomes coil and condense, and are in homologous pairs. Each homologous pair of chromosomes has four chromatids with centromere. Spindle fibers connect to centromere. Nuclear envelope and nucleolus disassociate. Each closely associated pair of chromosomes exchange parts = crossing-over. © McGraw Hill (a-b) © Biophoto Associates/Science Source 9  Crossing Over in Prophase l Chiasmata form where arms of chromosomes touch. Results in exchange of DNA by two parents © McGraw Hill 10  Metaphase l Chromosomes align in pairs at equator. Spindle formation completed. Access the text alternative for slide images. © McGraw Hill 11  Anaphase l and Telophase l Anaphase I One whole chromosome from each pair migrates to a pole. Telophase I Original cell becomes two cells or two nuclei. © McGraw Hill (c-d) © Biophoto Associates/Science Source 12  The Phases of Meiosis Division II Prophase II Chromosomes become shorter and thicker. Metaphase II Centromeres become aligned along equator. New spindles completed. Anaphase II Centromeres and chromatids of each chromosome separate, and migrate to opposite poles. © McGraw Hill (e) © Biophoto Associates/Science Source 13  Telophase II Telophase II Coils of chromatids relax and chromosomes become longer and thinner. Nuclear envelope and nucleoli reappear for each group of chromosomes. New cell walls form. © McGraw Hill (f) © Biophoto Associates/Science Source 14  Alteration of Generations 1 Meiosis results in half the number of sets in a gamete compared to the original parent cell. Haploid (1x) - Cell with one set of chromosomes Gametes Diploid (2x) - Cell with two sets of chromosomes Zygote Polyploid - Cell with more than two sets of chromosomes Triploid (3x) - Three sets of chromosomes Homologous chromosomes cannot pair properly, thus gametes typically inviable. Navel oranges, seedless watermelons © McGraw Hill 15  Alteration of Generations 2 Hexaploid (6x) - Six sets of chromosomes Bread wheat Octaploid (8x): 8 sets of chromosomes Strawberries Alternation of generations - Life cycle involving sexual reproduction that alternates between diploid sporophyte phase and haploid gametophyte phase © McGraw Hill 16  Sporophytes Sporophytes develop from zygotes and produce sporocytes. Sporocyte undergoes meiosis - Produces 4 haploid spores Access the text alternative for slide images. © McGraw Hill (Top Right) © Shutterstock/jaroslava V 17  Gametophytes Gametophytes develop from spores. Form cells or sexual structures in which gametes are formed by mitosis Fertilization produces zygote. Fertilization = Fusion of gametes Access the text alternative for slide images. © McGraw Hill (Top Right) © McGraw-Hill Education/ Richard Gross, photographer 18  Organisms with Alternation of Generations Alternation of generations - The basic plan can be seen in the: Protistan Fungal, and Plant Kingdoms. It becomes most conspicuous, however, in the Plant Kingdom © McGraw Hill 19  Rules for Alteration of Generations 1. First cell of gametophyte generation is a spore, and last is a gamete. 2. Any gametophyte cell contains half the chromosomes as the sporophyte generation. 3. First cell of sporophyte generation is a zygote, and last cell is a sporocyte. Access the text alternative for slide images. © McGraw Hill 20  Alteration of Generations Rules 4. Any sporocyte cell contains twice as many chromosomes as the gametophyte generation. 5. Change from sporophyte to gametophyte generation occurs as a result of meiosis. 6. Change from gametophyte to sporophyte occurs as a result of fertilization. Access the text alternative for slide images. © McGraw Hill 21  End of Main Content Because learning changes everything. ® www.mheducation.com © 2021 McGraw Hill. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill.