Presentation on theme: "Mitosis and Meiosis SC.912.L.16.17 Compare and contrast mitosis and meiosis and relate to the processes of sexual and asexual reproduction and their consequences."— Presentation transcript:
1Mitosis and MeiosisSC.912.L Compare and contrast mitosis and meiosis and relate to the processes of sexual and asexual reproduction andtheir consequences for genetic variation.
2Cell Division Process by which new cells form from existing cells Types of cell divisionThe First is cell division in prokaryotes, such as bacteria (Binary Fission).Eukaryotes use the second kind of cell division to grow and to repair their bodies (Mitosis).The third type of cell division occurs in eukaryotes. This form of cell division (Meiosis) produces the specialized cells involved in reproduction.
3Prokaryotic Cell Division Prokaryotes reproduce by binary fission.Steps of binary fission (relatively simple)The cell’s genetic information (DNA) is copied.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 theparent cell.Bacteria reproduce by binary fission.
5Eukaryotic 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.
6The Cell Cycle Continuous process in which cells Grow Make copies of their chromosomes (DNA replication)Divide to form daughter cells.The three main Phases are:InterphaseMitosisCytokinesis
7Phases of the cell cycle INTERPHASEThe cell spends most of its life in interphase, growing and preparing to divide.MITOSISThe nucleus divides into two nucleiCYTOKINESISThe cell membrane pinches in and the cytoplasm divides, forming two cells
8INTERPHASE The cell spends most of its life in interphase, growing and preparing to divide. Interphase has three parts G1 phase, S phase and G2 phaseG1 phase(Cell growth)S phase(DNA replication)G2 phase(Preparation for Mitosis)The cell grows and carriesout routine functions.It takes nutrients and usesthem for energyGrowthRepairs damaged organellesThe cell increases in sizeThe 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.
9Mitosis The cell divides into two nuclei Mitosis The cell divides into two nuclei. Mitosis ensures that each new cell receives a copy of each chromosomes. Mitosis has four phasesProphaseMethaphaseAnaphaseTelophaseChromatin condenses to form the chromosomes.Pairs of sister chromatics are attached at regions called centromeres.The nuclear membrane breaks downCentrioles separate and travel to opposite poles of the cellSpindle fibers form and organized themselves around the centrioles and attach themselves to the centromeres.Chromosomes line up along the middle of the cellEach 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 unravelThe spindle fibers break down.The nuclear membranes reforms around the chromosomes at each pole.
13The 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
14Asexual Reproduction The production of offspring by a single parent The offspring is genetically identical to the parentTypes of Asexual reproductionBinary 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
15Sexual ReproductionCells from two parents join to form a new individualOffspring 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.
16MeiosisMeiosis 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
17Stages of MeiosisMEIOSIS I Prohase I Metaphase I Anaphase I TelophaseI Cytokinesis I MEIOSIS II Prohase II Metaphase II Anaphase II TelophaseI I Cytokinesis II
18MEIOSIS IProphase IHomologous 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
19Metaphase IThe 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.
20Anaphase ISpindle fibers separate the paired homologous chromosomes and pull toward the oppsosite ends of the cell.Telophase I and Cytokinesis IThe cell divides to produce two daughter cells, each with a complete set of chromosomes.
21MEIOSIS IIThe two daughter cells divide again, to form four haploid cellsEach haploid cell has a unique set of chromosomes
22SC.L16.17 Compare and Contrast Mitosis and meiosis FeatureMeiosisMitosisDefinitionA 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 bodyType of cell producedSex cell known as gametes(egg and sperm)Body cell (blood cells, epithelial, muscle, nerve cells etc)Type of ReproductionSexualAsexualDaughter cells are GeneticallyDifferent from parent cell(shows genetic diversity)Identical to parent cell(exact replica of parent cell)
23Continuation…. Feature Meiosis Mitosis Crossing over Yes, mixing of chromosomes can occurNo, crossing over cannot occurParing of homologous chromosomesYes, homologous chromosomes separate and produce 4 haploid daughter cells.NoBeginning cellDiploid cellNumber of cells produced42Number of chromosomesHalf the original cellSame as original cellEnd product4 Haploid cells(the cells show genetic diversity)2 diploid cells(an exact replica of the parent cell)IIIIIIIIIIII
24Similarities 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)
26Comparing Methods of Reproduction Asexual ReproductionSexual ReproductionAdvantagesProduce many organisms quicklySince offspring are genetically diverse, they may be able to survive in more varied conditions.DisadvantagesNo genetic variationA factor such a toxin in the environment that harms one offspring can harm all of themNeeds to find a mateProduces relatively few offspring