Microsatellites, contd.
Note that the differences seen (the polymorphisms) between organisms are due to the number of repeats, which leads to a difference in size of the amplified products (ie. The length of the DNA segment between the 2 primers), not a difference in the DNA sequence per se.
In this example, the amplified fragment from A is shorter than that from B, because the AG motif is repeated fewer times. As a result, the A amplicon runs faster through the gel than the B amplicon, and the polymorphism is recognized by the different positions of the bands.
