In a particular population, over the course of several dozen generations, an adenine was replaced by a guanine at a particular non-coding locus in the dna base sequence. the evolutionary mechanism responsible for this change was?

Mutation

Explanation:

A Mutation alters the genetic message carried by that gene as there are permanent changes in the nucleotide sequence of DNA or a DNA gene.

This can occur by base pairs substitution, deletion or insertion

from my research i have to the conclusion that decomposers, such as fungi, bacteria and invertebrates, play a critical role in nutrient cycling and without them the earth's ecosystem may not support life as we know it. elements such as carbon, nitrogen and phosphorus exist in limited amounts on earth, although huge amounts of carbon are being released into the atmosphere from underground sources now by humans. it is still extremely important that other nutrients be retained by the process of re-use. decomposers are organisms that are able to chemically break down dead material and make these elements available for use by other organisms. without this breakdown of dead material, dead bodies would pile up. so decomposers also play a role in clean up also. without them, life might not continue as we know it and dead material would overwhelm the earth.    

lizards have adapted to life in the desert. some desert lizards have toes with spiny scales to them run across the sand without sinking. some use the sand to hide from predators, or to search for small animals that they prey upon.