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Middle School Science Room 212 – Miss Lida Lesson 2 / Explore – Page 129 “Asexual Reproduction” What is Asexual Reproduction? In asexual reproduction, one parent organism produces offspring without meiosis and fertilization. Because the offspring inherit all of their DNA from one parent, they are genetically identical to each other and to their parent. Types of Asexual Reproduction There are many different types of organisms that reproduce by asexual reproduction. In addition to fungi, bacteria, protists, and plants, and animals can reproduce asexually. Fission Cell division in prokaryotes that forms two genetically identical cells is known as fission. Fission begins when a prokaryote’s DNA molecule is copied. Each cop-y attaches to the cell membrane. Then the cell begins to grow longer, pulling the two copies of the DNA apart. At the same time, the cell membrane begins to pinch inward along the middle of the cell. Finally the cell splits and forms two new identical offspring. The original cell no longer exists. E.coli, a common bacterium, divides through fission. Some bacteria can divide every 20 minutes. Mitotic Cell Division Many unicellular eukaryotes reproduce by mitotic cell division. In this type of asexual reproduction, an organism forms two offspring through mitosis and cell division. Budding In budding, a new organism grows by mitosis and cell division on the body of its parent. The bud, or offspring, is genetically identical to its parent. When the bud becomes large enough, it can break from the parent and live on its own. In some cases, an offspring remains attached to its parent and starts to form a colony. The hydra goes through the process of budding and is an example of a multicellular organism that can reproduce asexually. Unicellular eukaryotes, such as yeast, can also reproduce through budding. Animal Regeneration Another type of asexual reproduction, regeneration, occurs when an offspring grows from a piece of its parent. The ability to regenerate a new organism varies greatly among animals. Producing New Organisms Some sea stars have five arms. If separated from the parent sea star, each arm has the potential to grow into a new organism. To regenerate a new sea star, the arm must contain a part of the central disk of the parent. If conditions are right, one five-armed sea star can produce as many as five new organisms. Sea urchins, sea cucumbers, sponges, and planarians can also reproduce through regeneration. Producing New Parts Regeneration of damaged or lost body parts is common in many animals. Newts, tadpoles, crabs, hydra, and zebra fish are all able to regenerate body parts. Even humans are able to regenerate some damaged body parts, such as the skin and the liver. This type of regeneration, however, is not considered asexual reproduction. It does not produce a new organism. Vegetative Reproduction Plants can also reproduce asexually in a process similar to regeneration. Vegetative reproduction is a form of asexual reproduction in which offspring grow from a part of a parent plant. Vegetative reproduction usually involves structures such as the roots, the stems, and the leaves of plants. In addition to strawberries, many other plants can reproduce by this method, including raspberries, potatoes, and geraniums. Cloning Cloning is a type of asexual reproduction performed in a laboratory that produces identical individuals from a cell or from a cluster of cells taken from a multicellular organism. Framers and scientists often use cloning to make copies of organisms or cells that have desirable traits, such as large flowers. Plant Cloning Some plants can be cloned using a method called tissue culture. Tissue culture enables plant growers and scientists to make many copies of a plant with desirable traits, such as sweet fruit. Also, a greater number of plants can be produced more quickly than by vegetative reproduction. Tissue culture also enables plant growers to reproduce plants that might have become infected with a disease. To clone such a plant, a scientist can use cells from a part of a plant where they are rapidly undergoing mitosis and cell division. This part of a plant is called a meristem. Cells in meristems are disease-free. Therefore, if a plant becomes infected with a disease, it can be cloned using meristem cells. Animal Cloning In addition to cloning plants, scientists have been able to clone many animals. Because all of a clone’s chromosomes come from one parent (the donor of the nucleus), the clone is a genetic copy of its parent. The first mammal cloned was a sheep named Dolly. Scientists are currently working to save some endangered species from extinction by cloning. Although cloning is an exciting advancement in science, some people are concerned about the high cost and the ethics of this technique. Advantages of Asexual Reproduction Asexual reproduction enables organisms to reproduce without a mate. Asexual reproduction also enables some organisms to rapidly produce a large number of offspring. For example, crabgrass reproduces asexually by underground stems called stolons. This enables one plant to spread and colonize an area in a short period of time. Disadvantages of Asexual Reproduction Asexual reproduction produces offspring that are genetically identical to their parent. This results in little genetic variation within a population. Another disadvantage of asexual reproduction involves genetic changes, called mutations, that can occur. If an organism has a harmful mutation in its cells, the mutation will be passed to asexually reproduced offspring. This could affect the offspring’s ability to survive.