Mutations at specific loci Stadler's method. L.J. Stadler studied frequencies of spontaneous mutations in maize for endosperm characters. The following steps were involved.
(i) A genetic stock dominant for several genes was grown as female parent and detasseled. Multipte recessive stock was sown on every 5th row to supply pollen.
(ii) Seed set on female plants was examined for endosperm characters e.g. shrunken. Most of the seeds showed dominant phenotype; the number of seeds showing recessive character represented mutations in female gametes.
Stadler also induced mutations artificially. For this purpose, he used irradiated pollen from dominant stock for pollinating recessive stock. Progeny showing recessive phenotype were classified as mutants, even though, atleast in some cases, these were later found to be due to deficiencies.
Singleton's method. W.R. Singleton also studied induced mutations. The pollen from plants dominant for several genes and growing in a field with radiation source were used to pollinate a rece'ssive stock growing in a field without radiation source. The pollen carrying mutations will give seeds, which will show recessive character in phenotype.
Mutations at unspecified loci
When a plant species is used where no marker stocks are available and the purpose is to study visible mutations in genome as a whole, the mutations are studied by segregation in M2 generation. The following steps will be involved :
- Irradiate the seeds.
Grow plants in M1 generation from irradiated seeds and self them. Harvest the seed in M1 on single plant basis.
Grow M2 on single plant progeny basis and
study segregation in M2 families. Each segregating family will represent one mutation in an irradiated seed.