Slide 1

SC.912.L.16.17 Compare and contrast mitosis and meiosis and relate to the processes of sexual and asexual reproduction and their consequences for genetic variation. Mitosis and Meiosis Slide 2 Cell Division Process by which new cells form from existing cells Types of cell division 1. The First is cell division in prokaryotes, such as bacteria (Binary Fission). 2. Eukaryotes use the second kind of cell division to grow and to repair their bodies (Mitosis). 3. The third type of cell division occurs in eukaryotes. This form of cell division (Meiosis) produces the specialized cells involved in reproduction. Slide 3 Prokaryotic Cell Division Prokaryotes reproduce by binary fission. Steps of binary fission (relatively simple) 1. The cells genetic information (DNA) is copied. 2. The cell then splits into two. Each cell receives a complete copy of the genetic information. This creates two new cells that are identical to the parent cell. Bacteria reproduce by binary fission. Slide 4 Slide 5 Eukaryotic Cell Division To give each cell the necessary genetic information, the cell most copy its chromosomes before it divides. Since eukaryotic cells have multiple chromosomes, the process of duplicating them is more complex than the copying of the single chromosome in an prokaryotic cell. Cell division is more complex in eukaryotic cells than in prokaryotic cells. Slide 6 The Cell Cycle Continuous process in which cells 1. Grow 2. Make copies of their chromosomes (DNA replication) 3. Divide to form daughter cells. The three main Phases are: 1. Interphase 2. Mitosis 3. Cytokinesis Slide 7 Phases of the cell cycle INTERPHASE The cell spends most of its life in interphase, growing and preparing to divide. MITOSIS The nucleus divides into two nuclei CYTOKINESIS The cell membrane pinches in and the cytoplasm divides, forming two cells Slide 8 INTERPHASE The cell spends most of its life in interphase, growing and preparing to divide. Interphase has three parts G 1 phase, S phase and G 2 phase G 1 phase (Cell growth) S phase (DNA replication) G2 phase (Preparation for Mitosis) The cell grows and carries out routine functions. It takes nutrients and uses them for energy Growth Repairs damaged organelles The cell increases in size The cells chromosomes are copied. The duplication of chromosomes is critical to normal cell function. If chromosomes are copied incorrectly, the change, or mutation, may affect the organisms in some way. The cell prepares the nucleus to divide. Produces extra organelles and cytoplasm. Slide 9 Mitosis The cell divides into two nuclei. Mitosis ensures that each new cell receives a copy of each chromosomes. Mitosis has four phases ProphaseMethaphaseAnaphaseTelophase Chromatin condenses to form the chromosomes. Pairs of sister chromatics are attached at regions called centromeres. The nuclear membrane breaks down Centrioles separate and travel to opposite poles of the cell Spindle fibers form and organized themselves around the centrioles and attach themselves to the centromeres. Chromosomes line up along the middle of the cell Each chromosome is attached to a spindle fiber at its centromere. The sister chromatids are pulled apart by the spindle fibers and begin to move to opposite poles of each cell. The chromosomes reach opposite poles of the cell and begin to unravel The spindle fibers break down. The nuclear membranes reforms around the chromosomes at each pole. Slide 10 Phases of Mitosis Slide 11 Cytokinesis Once mitosis is complete, the cell membrane pinches in and the cytoplasm divides, forming two cells that are identical to the parent cell. Slide 12 Slide 13 The Cell Cycle and Cancer In some cases a mutation can occur during the process, altering the cell cycle and causing new cells to form much more rapidly than normal. This leads to uncontrolled cell growth (cancer) Some cancers, such as skin cancer and lung cancers, are caused by mutations in body cells that affect the genes that control cell division. Most skin cancer is caused when ultraviolet (UV) radiation in sunlight damages skin cells. In most cases of lung cancer, genes are damaged by chemicals in tobacco products. Asbestos, radiation, and some air pollutants can also alter cells in ways that lead to lung cancer Slide 14 Asexual Reproduction The production of offspring by a single parent The offspring is genetically identical to the parent Types of Asexual reproduction Binary fission (for many single celled organisms like bacteria) Budding (In many multicellular) Cell division involving mitosis. A small bud grows off the parent organisms, this will eventually break off and become an independent organism) Many plants can reproduce from asexually from runners or other parts Slide 15 Sexual Reproduction Cells from two parents join to form a new individual Offspring produced are genetically different from parent. Sexual reproduction involves gametes, or sex cells. Gametes are haploid (they have half the number of chromosomes) Gametes form by Meiosis. Slide 16 Meiosis Meiosis is a process of cell division that reduces the number of chromosomes by half. When sex cells form the chromosomes are copied once. The nucleus then divides twice. The four cells that result have half as many chromosomes as a normal body cell Slide 17 Stages of Meiosis MEIOSIS I Prohase I Metaphase I Anaphase I TelophaseI Cytokinesis I MEIOSIS II Prohase II Metaphase II Anaphase II TelophaseI I Cytokinesis II Slide 18 MEIOSIS I Prophase I Homologous chromosomes pair up (process called synapsis) Crossing-over can occur. During crossing over, part of a chromatid on one chromosome breaks off and switches position with the matching portion on a chromatid of the homologous chromosome. Crossing-over increases the number of possible genetic combinations in the offspring Slide 19 Metaphase I The homologous pair line up along the center of the cell in a random fashion called independent assortment. Like crossing over, independent assortment leads to genetic variation. Slide 20 Anaphase I Spindle fibers separate the paired homologous chromosomes and pull toward the oppsosite ends of the cell. Telophase I and Cytokinesis I The cell divides to produce two daughter cells, each with a complete set of chromosomes. Slide 21 MEIOSIS II The two daughter cells divide again, to form four haploid cells Each haploid cell has a unique set of chromosomes Slide 22 SC.L16.17 Compare and Contrast Mitosis and meiosis FeatureMeiosisMitosis DefinitionA type of cellular reproduction in which the number of chromosomes are reduced by half. A process of asexual reproduction in which the cell divides in two producing a replica, (the number of chromosomes stays the same) FunctionSexual reproductionCellular Reproduction & general growth and repair of the body Type of cell producedSex cell known as gametes (egg and sperm) Body cell (blood cells, epithelial, muscle, nerve cells etc) Type of ReproductionSexualAsexual Daughter cells are Genetically Different from parent cell (shows genetic diversity) Identical to parent cell (exact replica of parent cell) Slide 23 Continuation. FeatureMeiosisMitosis Crossing overYes, mixing of chromosomes can occur No, crossing over cannot occur Paring of homologous chromosomes Yes, homologous chromosomes separate and produce 4 haploid daughter cells. No Beginning cellDiploid cell Number of cells produced 4 2 Number of chromosomesHalf the original cellSame as original cell End product4 Haploid cells (the cells show genetic diversity) 2 diploid cells (an exact replica of the parent cell) II IIII Slide 24 Similarities between mitosis and meiosis Both are forms of cell division. Both begin with diploid cells. Both occur within the nucleus of the cell. Both go through the same steps known as Prophase, Metaphase, Anaphase and Telophase. Both have in common cytokines is (The cytoplasm divides) Slide 25 Mitosis and Meiosis Slide 26 Comparing Methods of Reproduction Asexual ReproductionSexual Reproduction AdvantagesProduce many organisms quickly Since offspring are genetically diverse, they may be able to survive in more varied conditions. DisadvantagesNo genetic variation A factor such a toxin in the environment that harms one offspring can harm all of them Needs to find a mate Produces relatively few offspring