Hemoglobin (Hb) is an iron-containing oxygen-transport protein localized in vertebrate red blood cells (i.e., erythrocytes). Moreover, the heme group is a component of the Hb protein which is capable of binding or releasing molecular oxygen. Hb consists of four globular protein subunits, and each subunit contains a heme group. This group (heme) binds to an oxygen molecule in a manner that each Hb protein can bind to four oxygen molecules in order to transport them throughout the bloodstream.
Answer: Natural selection can act on traits determined by alternative alleles of a single gene ... hope this helps, this is one of many answers for this question!
