Hemoglobin by molecules such as carbon monoxide (for example, from tobacco smoking, exhaust gas, and incomplete combustion in furnaces). CO competes with oxygen at the heme binding site. Hemoglobin's binding affinity for CO is 250 times greater than its affinity for oxygen, meaning that small amounts of CO dramatically reduce hemoglobin's ability to transport oxygen. Since carbon monoxide is a colorless, odorless and tasteless gas, and poses a potentially fatal threat, carbon monoxide detectors have become commercially available to warn of dangerous levels in residences. When hemoglobin combines with CO, it forms a very bright red compound called carboxyhemoglobin, which may
Fetal hemoglobin hemoglobin) to readily transfer its oxygen to the fetal bloodstream. After the first 10 to 12 weeks of development, the fetus' primary form of hemoglobin switches from embryonic hemoglobin to fetal hemoglobin. At birth, fetal hemoglobin comprises 50-95% of the infant's hemoglobin. These levels decline after six months as adult hemoglobin synthesis is activated while fetal hemoglobin synthesis is deactivated. Soon after, adult hemoglobin (hemoglobin A in particular) takes over as the predominant form of hemoglobin in normal children. However HbF has been traced even in adults' blood (< 1% of all hemoglobin). Certain genetic abnormalities can cause the switch