Through evolution, hemoglobin oxygen affinity has been altered in species that live in different environments. Hemoglobin is the blood protein that carries O2 from the lungs to the tissues, and returns CO2 (from the tissues) to the lungs. Members of the family Testudinidae (turtles and tortoises) live under different environmental conditions and thus experience different oxygen levels. The hemoglobin of adult turtles is comprised of α- globin (alpha-D and alpha-A) and β-globin. For this research, hemoglobin of the terrestrial African spurred tortoise (Geochelone sulcata) and the aquatic painted turtle (Chrysemys picta) were analyzed. The African spurred tortoise lives in the hot, arid environments such as the Sahara, while the painted turtle live in calm freshwater environments, with muddy water bottoms. Analyses of the hemoglobin proteins were done through reverse-transcriptase polymerase chain reaction (RT-PCR) using primers designed for turtle globin genes. PCR products were then cloned and grown on selective media, and sequenced. Sequences were translated into amino acids and analyses were conducted to determine if differences in particular amino acid residues could be important in affecting the oxygen affinity of the hemoglobin protein.