how do mutations affect an organism? how do mutations affect an organism? they may cause the development of a disease-causing allele they may cause the development of a more beneficial allele they, in some cases, may have no noticeable affect all of the above request answer part b dna replication occurs at an unbelievably fast rate. once replication is complete, we can expect to find a number of mistakes. dna replication occurs at an unbelievably fast rate. once replication is complete, we can expect to find a number of mistakes. average large small