Jaderis writes:
My original idea was that there can be certain mutations that exist without selective pressure because they do not directly affect the survival of the individual or species
Firstly, all mutations occur 'without selective pressure' - selection is something exerted after the fact of their expression in phenotypes. But otherwise you are correct so far. Many mutations occur and then persist simply because they have no direct effect on the individual's survival - under present circumstances. However, circumstances may subsequently arise where they do affect survival, either negatively or positively.
Jaderis writes:
Was it the chemicals that prompted the mutation
Some chemicals are mutagenic, but they typically cause random damage. Don't confuse resistance to noxious chemicals as something brought about by those same chemicals, because that's not how it works.
Jaderis writes:
...reoccuring mutation inherent in the species that had either no function or a deleterious effect prior to the introduction of the chemical
Here you are much closer to the truth. Resistance to noxious chemcials is a result of selection by those chemicals on individuals bearing mutations that are otherwise neutral or deleterious in the absence of the chemical. However, the
production of the mutation itself has nothing to do with exposure to the chemical.
Jaderis writes:
... a truly random mutation occuring at just the right time
Precisely. Only the mutation at the locus in question would occur every generation with a particular frequency
with or without exposure to the chemical. It is only consistent exposure to the chemical that causes it to increase in frequency in the population, so its not as fortuitous as you might seem to imply by saying "at just the right time".
Edited by EZscience, : No reason given.