Melanism in the jaguar is conferred by a dominant allele, and in the leopard by a recessive allele. Melanistic and non-melanistic animals can be littermates. It is thought that melanism confers a selective advantage under certain conditions since it is more common in regions of dense forest, where light levels are lower. Preliminary studies also suggest that melanism might be linked to beneficial mutations in the immune system. Due to the excess black pigments, the typical spotted markings are present, but hidden, which is called "ghost rosettes".