This representation of an agarose gel shows how restriction enzyme digestion can be used to distinguish between an individual who is homozygous for a normal version of a gene versus individuals homozygous or heterozygous for a mutation in that gene. In this case the mutation creates a new restriction enzyme site. The normal piece of DNA is 200 base pairs long and lacks the restriction enzyme site, so it is not cut by the enzyme. The DNA with the mutation has the restriction enzyme sit, so it is cut into two pieces of 180 and 20 base pairs. Lane 2: Individual with the normal gene; only the 200 base pair DNA is seen. Lane 3: Individual heterozygous for the mutation; the normal 200 base pair DNA and the 180 and 20 base pair pieces are seen. Lane 4: Individual heterozygous for the mutation; only the 180 and 20 base pair pieces are seen.
