Crotamine

Crotamine likely evolved from beta defensin genes through a combination of gene duplication, regulatory mutation, and coding sequence mutation. Gene duplication must have occurred first because the initial gene, beta defensin, is a gene critical to an organism's function therefore that gene must be conserved. When an ancestor had two copies of the beta defensin gene, one of the copies then had a spontaneous mutation in the regulatory sequence, expressing beta defensin in the fangs at higher concentration. This evolutionary step might have happened before, after, or at the same time as a series of mutations in the coding sequence of the copied beta defensin gene in order to code for a poisonous protein instead.