The Recessive Inheritance

The thalassemias are a group of recessively inherited conditions. Recall that genes come in pairs. In recessive conditions, both members of the pair associated with the condition must be changed, or mutated. This is different from a dominant condition, in which only one copy of the gene need be changed in order to manifest symptoms.

In recessive conditions, a benign trait or carrier state can exist in which an individual has both a normal and a mutated copy of the gene. The term "normal" is a convention to simply describe the copy of the gene, called an allele, that is seen most often in the general population. The normal allele is able to compensate for the missing or altered function of the mutant allele. Therefore, the individual with trait does not have the symptoms seen in the disease. It is generally thought that each one of us carries 7-8 of these recessive traits, which would cause disease if present in a “double dose.”

It is not uncommon for a person with a recessive disease to be the first individual in his or her family to have the condition. Typically, this occurs when both parents are carriers of the trait. This is different from a dominantly inherited condition in which members of a family in several consecutive generations are affected.

Some Recessive Conditions
Attached earlobes
Sickle cell anemia
Cystic Fibrosis
Thalassemia

Some Dominant Conditions
Tongue rolling (try it)
Huntington's disease

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