The first type of molecular marker developed and run on gel electrophoresis were allozymes. These markers are used for the detection of protein variation. The word "allozyme" (also known as "alloenzyme") comes from "allelic variants of enzymes." When run on a gel, proteins are separated by size and charge. Although allozymes may seem dated when compared to the other markers available, they are still used today, mainly due to their low cost. One major downside is that since there is only a limited amount available, specificity an issue.