The loss of legs in snakes and other squamates is another good example of genes changing their expression pattern. In this case the gene Distal-less is very under-expressed, or not expressed at all, in the regions where limbs would form in other tetrapods.[4] In 1994, Sean B. Carroll's team made the "groundbreaking" discovery that this same gene determines the eyespot pattern in butterfly wings, showing that toolbox genes can change their function.[5][6][7]