Final answer:
Sickle cell trait is characterized by the presence of only one mutated β-chain. The other characteristic of sickle cell trait is normal red blood cell production.
Step-by-step explanation:
Sickle cell trait is characterized by the presence of only one mutated β-chain. The other characteristic of sickle cell trait is normal red blood cell production. In sickle cell trait, individuals have both normal and sickle-shaped red blood cells, but the presence of the mutated β-chain does not affect the overall production of red blood cells.