Expert: K Shows - 6/21/2005

Question
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Followup To
Question -
could u tell me where thalasemia, a genetic disorder, originated from. Since it is genetic, who is the first carrier?
Answer -
bg,

Thalassemia is a genetic disorder of hemoglobin synthesis, so it affects the ability of the blood to carry oxygen to the lungs.  There are many different types of thalassemia that range from very mild to severe.  More severe types have a characteristic facial structure as well.

Most thalassemias are very common in and originate from the regions surrounding the Mediterranean Ocean, including parts of the European coast, Middle East, and Africa, regions of the world that are most ancient.  Thalassemias have been around for a long time, and there is no single "carrier" who is responsible for being the first; rather, several people probably received mutations randomly.  The Mediterranean regions are known for giving rise to new genetic syndromes, possibly because the areas are ancient, population dense, and near the equator (it is a theory that exposure to more UV light can cause more mutations in a population).

A genetic disease rarely has a single ancestor, but a single mutation within a family can have a single ancestor who then passes on a specific genetic change to offspring.  Most genetic diseases are represented by a variety of mutations within a single gene in different unrelated persons and so cannot have a single ancestor.  For example, if a disease can be caused by mutation A or mutation B and if a person with mutation A reproduces, then all of his offspring would have mutation A, not mutation B.

There are hundreds of mutations that cause thalassemia, and involve different genes, so no one mutation can be responsible for all cases of thalassemia.

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thx, but who is the first known carrier of thalassemia? and how is it that UV rays can cause cell mutations?

Answer
There is no way to know the first known "carrier" of thalassemia.  Furthermore, as I mentioned before, there are several mutations in several genes that cause thalassemia: the thalassemias are a group of disorders. So there are multiple "first carriers" for each new mutation.

UV radiation causes DNA to mutate or break through a process called thymidine dimers.  The cell has an enzyme that naturally corrects thymidine dimers, although when the DNA is replicated in cell division the DNA polymerase may misread the dimer and change the base that should be there, which generates a mutation.  So, the more UV exposure, the more risk for mutation.  However, the only mutations that would matter in terms of causing disease would be in germline cells, or eggs and sperm.  If a mutation occurred in an egg or a sperm, then it could be passed on to the person's offspring.