Human adult haemoglobin is actually a composite of four protein chains called globins, knotted around each other like an orgy of hagfish to form a beautifully functioning parcel. The sequence of amino acids in the chains shows that the four globins are closely related to each other, but they are not identical. Two of them are called alpha globins (each a chain of 141 amino acids), and two are beta globins (each a chain of 146 amino acids). These globins are encoded by genes on different human chromosomes: alpha on chromosome 11, beta on chromosome 16.
