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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.

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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:

1 Mitosis and Meiosis SC.912.L Compare and contrast mitosis and meiosis and relate to the processes of sexual and asexual reproduction and their consequences for genetic variation.

2 Cell Division Process by which new cells form from existing cells
Types of cell division The 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.

3 Prokaryotic 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 the parent cell. Bacteria reproduce by binary fission.


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.

6 The 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: Interphase Mitosis Cytokinesis

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

8 INTERPHASE The cell spends most of its life in interphase, growing and preparing to divide. Interphase has three parts G1 phase, S phase and G2 phase G1 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.

9 Mitosis 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 phases Prophase Methaphase Anaphase Telophase 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.

10 Phases of Mitosis

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.


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

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

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.

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

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

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

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.

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.

21 MEIOSIS II The two daughter cells divide again, to form four haploid cells Each haploid cell has a unique set of chromosomes

22 SC.L16.17 Compare and Contrast Mitosis and meiosis
Feature Meiosis Mitosis Definition A 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) Function Sexual reproduction Cellular Reproduction & general growth and repair of the body Type of cell produced Sex cell known as gametes (egg and sperm) Body cell (blood cells, epithelial, muscle, nerve cells etc) Type of Reproduction Sexual Asexual Daughter cells are Genetically Different from parent cell (shows genetic diversity) Identical to parent cell (exact replica of parent cell)

23 Continuation…. Feature Meiosis Mitosis Crossing over
Yes, 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 cell Diploid cell Number of cells produced 4 2 Number of chromosomes Half the original cell Same as original cell End product 4 Haploid cells (the cells show genetic diversity) 2 diploid cells (an exact replica of the parent cell) II II I I I I II II

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)

25 Mitosis and Meiosis

26 Comparing Methods of Reproduction
Asexual Reproduction Sexual Reproduction Advantages Produce many organisms quickly Since offspring are genetically diverse, they may be able to survive in more varied conditions. Disadvantages No 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

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