<P> Some normal hemoglobin types are; Hemoglobin A (Hb A), which is 95 - 98% of hemoglobin found in adults, Hemoglobin A2 (Hb A2), which is 2 - 3% of hemoglobin found in adults, and Hemoglobin F (Hb F), which is found in adults up to 2.5% and is the primary hemoglobin that is produced by the fetus during pregnancy . </P> <P> Hemoglobin variants occur when there are genetic changes in specific genes, or globins, that cause changes or alterations in the amino acid . They could affect the structure, behavior, the production rate, and / or the stability of that specific gene . Usually there are four genes that code for alpha globin and two genes that code for beta globin . If the genes for alpha chains is mutated, the most common condition that occurs is alpha thalassemia, which causes a decrease in production of that gene . The level of severity of alpha thalassemia is determined by the number of genes that are affected . </P> <P> Hemoglobin variants are most often inherited characteristics . First, abnormal beta gene can be inherited in an autosomal recessive fashion . This means that the person who inherits this will have two copies of the altered gene . Both of these genes can be passed to offspring . The next way they can be inherited is in a heterozygous fashion . This means that the person has one normal beta gene and one abnormal beta gene . This person is considered to be a carrier of whichever hemoglobin variant is inherited . Only the abnormal gene can be passed on to offspring in this case . Carriers also do not have to deal with having symptoms or any health concerns . Another way that beta genes can be inherited is in a homozygous fashion . This means that the person has two abnormal beta genes . In this case the person produces the associated hemoglobin variant and may have the symptoms and complications that are associated with they specific hemoglobin variant they have . The severity of the conditions mainly depend on the genetic mutation and it may vary from person to person . The copies of the abnormal beta genes would more than likely be passed to offspring . </P> <P> Along with lengthy list of common hemoglobin variants, there are some variants that are less common . These variants are considered silent, which means that they have no signs or symptoms . They usually affect the functionality and / or the stability of the hemoglobin molecule . With most of these variants are mutations in the alpha globin gene that result in an abnormally long alpha chain and an unstable hemoglobin molecules . </P>

Any abnormal change in the structure or function which produces symptoms is considered a(n)