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Name: Bevan C.
Status: Student
Age: 15
Location: N/A
Country: N/A
Date: August 2002

Bevan, keep in mind that you generally have two "good" copies of every gene, one from your mother and one from your father. In many cases, your cells can function fine as long as at least one copy is ok. So, even if you inherit a mutated copy from one parent, you are usually still ok, since the normal copy encodes enough normal protein to get the job done. The disease is recessive because you have to have two "bad" mutated copies of the gene before you see ill effects. Keep in mind that by "mutated", here I am referring to a gene that makes either no protein, or a non-functional protein *that does not interfere with the function of the normal protein.*

However, there are cases of diseases where one bad copy can cause a disease. Let us say a mutation causes a protein to be made that actually interferes with the normal function of the cell. Maybe a mutation causes too much of the protein to be made, or a mutation causes the protein to fold in a way that it acts like the proverbial "monkey wrench" thrown into a machine. This would be a case of a disease caused by a dominant mutation, since the presence of the other, normal copy of the gene cannot overcome the problem created by the mutant copy.

In purely statistical terms, there are many more possibilities to have a mutation that knocks out the function of a protein, than there are ways to have a mutation that causes a dominant, "crazy-acting" protein. So, more diseases arise from recessive mutations than from dominant mutations.

Paul Mahoney, PhD


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