Final answer:
Reticulocytes are immature red blood cells that mature into erythrocytes. In mature adults, the percentage of reticulocytes among red blood cells is typically 1-2%.
Step-by-step explanation:
Reticulocytes are immature red blood cells that are released into the bloodstream, where they mature into erythrocytes (mature red blood cells). Only a small percentage of reticulocytes are present in healthy adults, typically comprising 1-2% of the total erythrocyte count. Once reticulocytes mature, they lose their remnants of organelles such as ribosomes and become fully functional erythrocytes.