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| Parthenogenesis and Tissue Culture |
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| Parthenogenesis is a form of reproduction in which the ovum develops into a new individual without fertilisation. Natural parthenogenesis has been observed in many lower animals (it is characteristic of the rotifers), especially insects, e.g., the aphid. In many social insects, such as the honeybee and the ant, the unfertilized eggs give rise to the male drones and the fertilized eggs to the female workers and queens. In 1900, Jacques Loeb accomplished the first clear case of artificial parthenogenesis when he pricked unfertilized frog eggs with a needle and found that in some cases normal embryonic development ensued. Artificial parthenogenesis has since been achieved in almost all major groups of animals, although it usually results in incomplete and abnormal development. Numerous mechanical and chemical agents have been used to stimulate unfertilized eggs. In 1936, Gregory Pincus induced parthenogenesis in mammalian (rabbit) eggs by temperature change and chemical agents. No successful experiments with human parthenogenesis have been reported. The phenomenon is rarer among plants (where it is called parthenocarpy) than among animals. Unusual patterns of heredity can occur in partheogenetic organisms. For example, offspring produced by some types are identical in all inherited respects to the mother. |
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| Tissue culture is based on the concept of cellular totipotency. That is all the multicellular organisms basically are formed from a single cell (the zygote), by repeated multiplication and differentiation. Thus a single cell can develop into a whole organism or in other words, the cell is totipotent. This is because it contains the full set of genetic information needed to make the organism. This is called cellular totipotency. |
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| Thus, a tissue can be taken from any part of the plant and put in a suitable nutrient medium. The nutrient medium is jelly-like and is taken in a test-tube. The tissue starts dividing mitotically and produces a mass of cells. This structure is undiferentiated and is called the callus. |
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| Tissue Culture |
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| Differentiation refers to the formation of different tissues like the roots, stem, leaves, etc. The callus is transferred to other medium that contains different hormones for differentiation to occur. This differentiated mass of tissue is called the embryoid which grows into the new plantlet. The plantlets are then planted in pots and then in the fields. |
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| Here are some terms used in cell and tissue culture. |
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| The cells/tissues of the plant used for culture is called the explant. The undifferentiated mass of cells obtained from the single cell is called the callus. |
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| The embryo got from the culture is called the embryoid. |
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| The plant developed from embryoid is called the plantlet. |
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| This method of propagation is also called micropropagation since it uses only a small part of the plant. A single cell can also be separated and cultured to give rise to a new plantlet. This is called cell culture. |
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