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Changes in genetic material are called mutations. They can be neutral in effect, disease producing, or rarely protective. Polymorphisms are variations in the DNA sequence that occur at a frequency of more than 1%. These mutations are less frequent in coding regions of the gene and are much more commonly found in introns or between genes. Different types of DNA variations include restriction fragment-length polymorphisms (RFLPs) (5), single nucleotide polymorphisms (SNPs) (6), variable number of tandem repeat polymorphisms (7), and microsatellite markers. SNPs are the most common of these, occurring as often as once in every 100 to 300 base pairs. Typically, polymorphisms do not produce disease, although in some cases, a polymorphism can increase a person’s disease susceptibility. Polymorphisms are helpful for following the inheritance of a nearby gene through families, as well as for studying the genetic susceptibility to certain complex diseases (8).

Deoxyribonucleic acid (DNA), the genetic material, is a double helical structure consisting of four bases (adenine, guanine, cytosine, and thymine) on a sugar-phosphate backbone. DNA replication occurs through a semiconservative mechanism; the double helix separates and new strands form using the previous strands as templates. During replication, cytosine will pair only with guanine, and adenine will bind only with thymine. DNA is converted to ribonucleic acid (RNA) by transcription, and RNA is converted to a protein by translation. A set of three bases codes for an amino acid; therefore, the bases make up a code that determines the entire protein’s amino acid sequence. The structure of a gene consists of exons (the portion of the sequence that is translated to protein) and introns, or intervening sequences.