Somatic Mutation:
These are sudden alterations appearing in the somatic characters of an individual. Such mutations normally do not affect the entire plant and express themselves only in those regions where a cell has undergone change.
Certain varieties of apples and navel orange are examples of this. Somatic mutations also occur in Snapdragons, when a white flowered variety produced red flowers in a single blossom.
Another kind of mutation, which has much significance from the point of view of Horticulture, is the bud mutation. In this, few cells of the bud or the entire bud (if mutation has occurred quite early) shows mutated characters, when grown into a flower or a vegetative branch.
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If the mutation has occurred a little late during the development of the bud, the flower or the vegetative branch will be a mosaic of normal and mutant characters. Such a combination of two genetically non identical tissues is called a Chimaera.
Chimaeras have been seen in Geranium (Pelargonium zonale) in which a branch bears both green and white leaves. Another example of bud mutation is that of nectarine mutation in which the skin of the fruits is smooth instead of being rough. Smooth skin is recessive to rough skin.
There are numerous examples of somatic mutations in animals also; for e.g. white eyes, vestigial wings etc. of Drosophila.
Germinal Mutations:
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Mutations occurring in the reproductive cells are called germinal mutations. They are heritable and consequently they affect the whole of the organism in the next generation. Germinal mutations are called gametic when they occur in gametes and zygotic when they occur in the zygote.
The gametic mutation will express itself readily when either the mutation is dominant or if recessive two mutant gametes should unite. Zygote mutations on the other hand express themselves readily. The ancon breed sheep is a typical example of germinal mutation.