According to Hugo De Vries, speciation is due to

Genetic drift occurs due to . . . . . . .

The peppered moth $(Biston \text{ } betularia)$, the black-coloured form became dominant over the light-coloured form of moth in England during the industrial revolution. This is an example of

Random genetic drift in a population probably results from

Which technique is used to prove that antibiotic-resistant bacterial mutants are pre-existing and not induced by the environment?

In a population of plants,some were extremely tall,and the remaining were extremely dwarf. No plants of the population showed intermediate height. The type of operation of natural selection in the above case is