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Topic 6: Reproduction 6-1: Mitosis & Asexual Reproduction
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In cell division, the chromosomes are equally divided into two new cells Each new cell is identical to the parent cell The division of the chromosomes is called mitosis After mitosis, the cytoplasm of the cell divides in the process of cytokinesis Cell Division
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Mitosis (mitotic cell division): produces identical cells; a clone to the parent cell Multicellular Organisms (many cells) Regeneration of Cells/Body Parts Lost; hydra, flatworm, starfish Growth, Development, Replacement & Repair of Cells; large animals, humans Unicellular Organisms (single- celled) Asexual Reproduction: produces a genetically identical offspring; amoeba, bacteria Why Do Cells Divide?
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Mitosis (mitotic cell division): produces identical cells; a clone to the parent cell Multicellular Organisms (many cells) Growth, Development, Replacement & Repair of Cells; large animals, humans Unicellular Organisms (single-celled) Asexual Reproduction: produces a genetically identical offspring; amoeba, bacteria Why Do Cells Divide? Regeneration of Cells/Body Parts Lost; hydra, flatworm, starfish
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One parent Produces a genetically identical offspring (clone) Offspring (daughter cell) has the exact same DNA as the parent cell Number of chromosome is identical (diploid, 2n) Diploid: cells with sets of chromosomes in pairs of 2 Advantage: many offspring may be produced quickly Disadvantage: there is NO VARIATION Asexual Reproduction
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Single-celled organisms divide asexually as a means of reproduction Human cells perform asexual reproduction to grow & repair. Remember…
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Mitosis: chromosomes duplicate, form 2 nuclei, and split into 2 identical cells Cells divide in order to multiply Division = Multiplication
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Overview of Mitosis interphaseprophase metaphaseanaphasetelophase cytokinesis I mmediately P lease M ake A nother T wo C ells
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Mitosis in Real Time
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Interphase Interphase is the part of the cell cycle when the cell grows and duplicates its chromosomes Occurs just before mitosis begins.
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Prophase The first stage of mitosis The chromosomes shorten and thicken The centrioles move to opposite ends of the cell The nuclear membrane breaks down and the nucleus disappears Centrioles Replicated chromosomes Nuclear membrane
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Metaphase The second stage of mitosis Spindle fibers are made by the centrioles The chromosomes line up across the middle of the cell The spindle fibers attach to the centromeres of the chromosomes Tip: Remember Middle / Metaphase Spindle
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Anaphase The third stage of mitosis The centromeres that connect the chromatids divide (move apart) The spindle fibers move the chromatids to opposite ends of the cell Tip: Remember Anaphase / Apart
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Telophase The last stage of mitosis Each end of the cell now has an identical set of chromosomes Nuclear membranes form around each set of chromosomes Cytokinesis can now occur Nuclear membrane
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Cytokinesis In animal cells, the cell membrane pinches in the middle to form a cleavage furrow When the pinching in is complete, two identical daughter cells are formed Cleavage furrow
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In plant cells, a cell plate is used instead of a cleavage furrow The cell plate grows in the middle of the cell and will become a new cell wall Cytokinesis
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Budding in Hydra & Yeast
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Regeneration
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Binary Fission
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Since asexually produced offspring are clones of the parent cell, there is no variation within the population. If there is a change to the environment, they may not be able to adapt to changes or survive. However, if the parent has a trait with high adaptive value (genes that allow it to survive), it will be passed on to the next generation. Ex: resistance to antibiotics, pesticides, etc. Disadvantage: No Variation
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Cancer Cancer cells show uncontrolled cell division They grow even when there is no more room and forms a mass called a tumor Tumors steal energy and nutrients from normal tissues Benign tumors stay in their original location and do not spread
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Cancer Malignant tumors spread throughout the body when cancer cells break off from the tumor and travel in the blood The spread of cancer is called metastasis All body tissues can be affected with cancer Cancer is caused by mutations in DNA Substances that cause these mutations that lead to cancer are called carcinogens
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Mitosis in whitefish embryo
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Mitosis in plant cell
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onion root tip
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Mitosis Video
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