The agency which brings about spontaneous mutations is not known. They apparently occur due to natural causes. The first recorded instance of a spontaneous mutation is that of the Ancon breed sheep.
A detailed study of the spontaneous mutation in Drosophila melanogaster, is that of T.H. Morgan, where he described the sudden appearance of white eyed flies in a population of red eyed individuals. Some of the spontaneous mutations noticed in plants and animals are as follows.
1. Spontaneous mutations in plants:
1) Double petunia,
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2) Double rose,
3) Shirley poppy,
4) Single flower mutant in sunflower,
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5) Multi-leaf formation in tobacco reported by Hayes,
6) Reduction in ray size in the ray florets in Bidens pilosa of Composite (reported by the author)
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2. Spontaneous mutations in animals:
1) Polydactyly in man, sheep, cats etc.
2) Multinippled condition in sheep,
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3) Silky fowls,
4) Albinism in man, pig, pigeon, rodents etc.
5) Double cared cattle,
6) Mule footed swine,
7) White canaries,
8) Hornless cattle,
9) Hares’ lip in man,
10) Widows peak in man,
11) Lobster claws in man,
12) Cleft palate in man etc.
Spontaneous mutations are generally rare and may be of two types dominant and recessive. Usually recessive mutations are more frequent than dominant mutations.