Classification of mutations
A) Based on origin
- Spontaneous mutations :
- Mutations occur in natural populations at a low rate (10-6) but different genes may show different mutation rates.
- For example : in maize R-locus mutates at the frequency of 4.92 x 10-4 i.e. (1 in 20000 population), when as Su locus at 2.4 x 10-6 ( 1 in 25 lakhs).
- The Wx locus considered to be highly stable.
- The difference in mutation rate may be due to a) Genetic back ground i.e. presence of mutator genes b) Genes themselves c) Environment
2.Induced mutation :
- Mutations may be artificially induced by treatment with certain physical or chemical agents.
- Available evidence indicates that induced mutation rarely produces new alleles they produce alleles which are already known to occur spontaneously.
- Induced mutations are comparable to spontaneous mutations in their effects and in the variability they produce.
- Induced mutation occurs at a relatively higher frequency so that it is practical to work with them.
B) Based on magnitude of phenotypic effects
- Macro mutations:
- Oligogenic Mutation – Large phenotypic effect and recognizable on individual plant basis and can be seen easily in M2 generations.
- Ancon breed in sheep, pod maize to cob maize.
- Micro mutations :
- Polygenic mutations – Small phenotypic effect which cannot be recognized on individual plant basis but can be recognize only in a group of plants. Selection should be done in M3 or later generations.