According to the Modern Synthesis of Evolution mutational events occur spontaneously and are considered random in respect to the potential outcome they might inflict on the organism. In other words,  beneficial mutations could not be directly selected, but they occur by chance and are filtered by natural selection. For instance, the presence of an antibiotic does not direct mutations to genes that are related to antibiotic resistance. Instead, mutations occur prior to the bacterial contact with the antibiotic and the resistant mutants are then selected by the presence of the antibiotic in the medium. However, in the last 30 years … Continue reading Origin of PHO-constitutive mutants