mutations are caused by various factors. it mostly has to do with dna which creates proteins. im sure you've heard about DNA as the "blue-prints" for the whole of an organism. these 'blue-prints' must be copied everytime a cell divides. so as in sexual reproduction the process of Meosis "division of stem cell in order to create germ cells like sperm and ovum,(i belive)" can cause 'mutations' or messed up copies in these germcells that then go one to bind with their respective germcell partner to create another organism, but because of a mutation in one or both, the organism becomes a bit different from what either parents genetic material might have offered. and its dna has thus been mutated. as mentioned before, most of these mutations are small in the DNA and are practically meaningless to the organsim species to cause a verifiable change in its reproductive rate/success. genetic dna for the germ cells can be messed up and mutated by some viruses, some chemicals, forms of energy (UV), or just some unseen mess up in the copying process, etc. now asexual reproduction (as in bacteria) is probably simpler. as the bacteria's dna gets messup by a certain factor, it divides into two bacteria wich are genetically different from the more original form. so lets say there's bacteria that might die with a certain chemical. but before being exposed to the chemical it might grow in numbers and some of those bacteria might get dna changes that cause the bacteria to somehow make more, if not new, proteins/enzymes that help and heal it from the chemical. so when you use the chemical on this colony of bacteria, a few survive and go on to reproduce(divide and grow and divide again) and can make another colony of a large size. but when you use the chemical on these most, if not all, are able to survive. you can see that if the chemical had not been used, the resistant colony would like not have developed because the other bacteria in the colony were competeting for space. this is all in one species of bacteria(im not sure how scientists classify/separate these species as all they do is divide and mutate, so species differentiation must be measured by some basis other than reproduction, such as characteristics). it is also important to mention that many bacteria now have the ability to share dna with eachother, thus increasing their mutation rate/scope.
---not sure if any of that helped ur understanding of the concept of mutation.
