Fig. 4

A sample student's gel. At the top of the gel, the eye color of the sample is noted as W (white-eyed), R (red-eyed), or C (control, no DNA present in sample). On the left of the gel are the results for the Near marker, the marker located in close proximity to the eye color gene. The original red-eyed male had a high band at the Near marker. One can see that all red-eyed flies have the high band at the Near marker, illustrating the concept of a nearby neutral variant hitchhiking with an advantageous mutation (the red-eye color). On the right side of the gel are the results for the Far marker, which is located on the other end of the chromosome from the eye color gene. The Far marker clearly has less size differential between the high and low bands, so instruct students to us caution in interpreting results. The original red-eyed male had a low band at the Far marker, but one can see that red-eyed flies in the current sample have both high and low bands, illustrating the concept that recombination breaks up the association between the eye color gene and neutral variants located far away on the chromosome