Final answer:
Sickle cell anemia is an autosomal recessive disorder where two copies of the mutant allele are necessary for the manifestation of the disease. Carriers with one mutated allele (S) and one normal allele (A) can transmit the trait. Blood cell sickling shows codominance in the heterozygous state.
Step-by-step explanation:
The mode of inheritance of sickle cell anemia is autosomal recessive. This means that a person must inherit two copies of the mutant allele, one from each parent, in order to express the disease phenotype. Individuals carrying one normal allele (A) and one mutated allele (S) are considered carriers of the sickle cell trait. These carriers usually do not show symptoms of sickle cell anemia but can pass the allele to their offspring. When two carriers have a child, there is a 25% chance the child will inherit both mutated alleles, resulting in sickle cell anemia. The disease is characterized by red blood cells that take on a sickle or crescent shape, leading to issues such as clogged blood vessels and reduced oxygen delivery.
Furthermore, it is important to note that within the phenotype, sickle cell anemia demonstrates a characteristic known as codominance in blood cell sickling; this means that both normal hemoglobin (A) and sickle cell hemoglobin (S) can be expressed together in those who are heterozygous (AS), producing some sickle-shaped and some normal red blood cells. Sickle cell anemia is also associated with protection against malaria, which is why the trait is more common in regions where malaria is prevalent.