Genes produce genotype information that is translated to phenotype information, including eye and hair color, size and wing span. Although some human phenotypic characteristics are easy to observe, such as eye color, attached or detached earlobes and the presence or absence of a widow's peak, it is not easy to analyze the genotypic information producing these traits. While fruit flies do not share many characteristics with people, the biological process for eye-color determination is similar, so students can learn a lot about their own DNA by collecting and observing samples of fly eyes through chromatography.
The most important part of the chromatography process is spotting. Once a sample of fruit fly eye pigment is collected on a lab plate, it must be treated with a solution in order for colors of different densities to separate for analysis. Common spotting solutions include acetone, or an equal ratio of alcohol to ammonia. For best results, it is necessary to saturate the plated sample and wrap it tightly in aluminum foil, as air exposure can interfere with accurate chromatography maps.
Once a moving solvent is applied to a sample and wrapped in foil, the solution will mix with the fly eye pigments and cause the various colors to separate. While all fruit flies produce genotypic information for eye colors brown, blue, yellow and scarlet, they combine differently based on genetic mapping instructions to produce the scarlet, red, white and brown phenotypes. The difference in these genetics instructions is easily observed on a chromatography map, based on how many spots appear on the plate, as well as the distance between spots.
Freshly anesthetized Drosophila fruit flies are a good choice for a basic thin-layer chromatography experiment on eye pigmentation. Place the fly head on a thin-layer chromatography plate and carefully squish the insect's head, transferring the fly's eye pigment onto the plate. Remove the head and repeat with three additional flies. Add five drops of acetone to the plate for spotting. Wait 30 minutes before wrapping plates in foil and leaving for overnight processing. Observe and record spot numbers, colors and distance apart in a lab notebook. Consult a textbook or instructor to determine the fruit fly identities based on chromatography results.