Deficiency of hemoglobin due to defective gene; short life-span for RBCs Defective gene leads to abnormally shaped RBCs in conditions of low oxygen Damage to bone marrow due to toxic chemicals, radiation, and other factors Destruction of red blood cells; toxic chemicals are one possible cause Increase in RBCs that are large and fragile; due to deficiency in vitamin B-12.

Answers:

Thalassemia

Deficiency of hemoglobin due to defective gene; short life span for RBCs

Sickle cell disease

Defective gene leads to abnormally shaped RBCs n conditions of low oxygen

Aplastic Anemia

Damage to bone marrow due to toxic chemicals, radiation, and other factors 

Hemolytic Anemia

Destruction of red blood cells; toxic chemicals are one cause

Pernicious Anemia

Increase in RBCs that are large and fragile; due to deficiency in vitamin B12

Explanation:

Thalassemia

It is a blood disorder. It's known for its lower-than-normal levels of an oxygen-carrying protein with unusual lower amounts of red blood cells in the body.

Sickle cell disease 

It impairs the function of hemoglobin as the atypical hemoglobin molecules known as hemoglobin S, that alters red blood cells into a sickle, or crescent, shape.

Aplastic anemia

It is a rare but major blood disorder due to inability of the bone marrow to produce adequate new blood cells needed by the body.

Hemolytic anemia

It  is a result of anemia due to hemolysis, the unusual breakdown of red blood cells (RBCs), in the blood vessels (intravascular hemolysis) or spleen

Pernicious Anemia

It is a deduction in red blood cells due to inability of the body to take in adequate vitamin B12.

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