gene
You have learned that an allele is an alternative form of a gene. Most, if not all genes have alternative forms causing the resulting protein to function slightly differently. But are there alleles that cause proteins to function dramatically differently or not function at all? A mutation is a change in the DNA or RNA sequence, and many mutations result in new alleles. Some mutations have no effect on the protein, whereas others are either beneficial or harmful. In fact, evolution could not take place without the genetic variation that results from beneficial mutations. In humans, harmful mutations can result in genetic diseases. There are also chromosomal mutations, large changes with dramatic effects. See Mutations are changes in genetic information at http://www. dnaftb. org/27/animation. html for a description of the early work on mutations.