What Is PCR

DNA tests rely on two basics facts, 1) the distance a molecule of DMA moves in a thin slap or small column of gelatin-like material when an electric current is passed through it depends on the length of the piece of DNA, a process called electrophoresis and 2) single strands of DNA will bind to each other if they have complementary base sequences An A will pair with a T, a T with an A, a G with a C, and a C with a G. 

PCR is also used with specific probes to detect the presence of a virus or other infection in the blood or tissue and to determine how many virus particles are present. 

Many of these tests are automated so that a technician need only place the extracted DNA in a small tube, instruct the machine which tests to run, push a button, and wait for the printout. 

Huntington disease presents an enormous family challenge because the symptoms do not develop until later in life. The mutated gene is dominant (as opposed to recessive), which means that the risk of developing the disease is 100% for people who inherit just one copy of the mutated form of the gene. Children of a person with Huntington disease have a 50% chance of inheriting the mutated 

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