Question

which type of mutation is likely to have the least effect on an organism?

Answer 1

I am not sure what are you looking for, maybe silent mutation?

Answer 2

It changes the genotype but doesn't really affect the phenotype. One of the nitrogen bases was mutated into another, but still coding the same nucleic acid

example :
TTT was mutated into TTC, still they both coded the Phe, so, nothing really change in the phenotype.

For more explanation : http://education-portal.com/academy/lesson/silent-mutation-definition-example-quiz.html#lesson


P.S : sorry if this is not what you're really looking for as the answer, I'm just trying to help (: