Final answer:
Aplastic anemia is caused by a defect in the bone marrow, leading to a deficiency in RBC stem cells, as well as lower levels of white blood cells and platelets. It can be inherited or triggered by various factors and results in low quantities of blood-formed elements.
Step-by-step explanation:
Aplastic anemia is the type of anemia caused by a defect in the bone marrow. When the bone marrow is affected, not only red blood cells but also white blood cells and platelets are produced in lower quantities. This condition can be inherited or triggered by factors such as radiation, medication, chemotherapy, or infection. It results in a deficiency of RBC stem cells and can lead to low levels of blood-formed elements.