Final answer:
There are four variants of hemoglobin that have been identified: hemoglobin A, hemoglobin A2, hemoglobin F, and hemoglobin H.
Step-by-step explanation:
Hemoglobin is a protein found in red blood cells that carries oxygen throughout the body. There are actually four variants of hemoglobin that have been identified: hemoglobin A, hemoglobin A2, hemoglobin F, and hemoglobin H. Each variant has a slightly different structure and function. Hemoglobin A is the most common variant in adults, while hemoglobin F is primarily found in fetuses and infants.