mutation
One example of a gap gene is the Krüppel gene, which regulates the activity of a number of other genes. Krüppel literally means "cripple" in German, named for the crippled appearance of mutant larva. Gap genes are defined by the effect of a mutation in that gene, and Krüppel is one such effect. Other gap genes are known as tailless and knirps a "squirt or whippersnapper" . Gap genes encode transcription factors which directly effect the expression of additional genes involved in embryo segmentation, called the pair-rule genes . Pair-rule genes are expressed in alternating segments within the developing embryo. Pair-rule genes have very creative names, such as even-skipped, hairy, odd-skipped, odd-paired, sloppy paired and fushi tarazu , which is Japanese for few segments. See My favorite silly gene names at http://www. itsokaytobesmart. com/post/82318778810/funny-gene-names for a list of other interesting gene names.