(without oxygen). As hemoglobin F has 4 heme groups, it can bind to up to four oxygen molecules. It is composed of two ? (alpha) subunits and two ? (gamma) subunits, whereas hemoglobin A (97% of total hemoglobin in adults) is composed of two ? and two ? (beta) subunits.

In humans, the ? subunit is encoded on chromosome 16 and the ? subunit is encoded on chromosome 11. There are two very similar genes