True about polymorphism is

Polymorphism: (more fully genetic polymorphism) refers to the simultaneous occurrence in the population of genomes showing variations at a given position. The original definition applied to alleles producing different phenotypes. Now it is also used to describe changes in DNA affecting the restriction pattern or even the sequence. For practical purposes, to be considered as an example of a polymorphism, an allele should be found at a frequency > 1 % in the population. * There is a normal variation of DNA sequence just as is true of more obvious aspects of human structure. * Variations of DNA sequence, polymorphisms, occur approximately once in every 500 nucleotides, or about 107 times per genome. * There are without doubt deletions and inseions of DNA as well as single-base substitutions * In healthy people, these alterations obviously occur in noncoding regions of DNA or at sites that cause no change in function of the encoded protein. * This heritable polymorphism of DNA structure can be associated with ceain diseases within a large kindred and can be used to search for the specific gene involved, * RESTRICTION FRAGMENT LENGTH POLYMORPHISM (RFLP): The differences in DNA sequence cited above can result in variations of restriction sites