An allele is a variant form of a gene. some genes have a variety of different forms,which are located at the same position, or genetic locus, on a chromosome.
Carbon is the only element that can form so many different compounds because each carbon atom can form four chemical bonds to other atoms, and because the carbon atom is just the right, small size to fit in comfortably as parts of very large molecules. ... They can even join "head-to-tail" to make rings of carbon atoms.
