ANTXR2 and anthrax infection: For instance in humans, natural variation in expression levels of the gene CMG2 is associated with variation in resistance to anthrax (Martchenko et al. 2012), and in the fungus Suillus luteus, selection pressure from heavy metal pollution quickly led to copy number variation in transport genes with protective functions against heavy metal toxicity (Bazzicalupo et al. 2019).