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Sequence Analysis of Single Polymorphism in the Factor V Gene - page 1 / 15





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Biol  420                                                                                                                                          Fall 2007

Sequence Analysis of Single Polymorphism in the Factor V Gene


To use DNA from your cheek cells to determine whether you have a normal or mutated Factor V gene.

To develop an understanding and appreciate the usefulness of polymerase chain reaction (PCR) and sequencing.


Today it is common practice to use diagnostic tests to screen genetic diseases. Many genetic diseases are caused by single base pair mutations called polymorphisms.  In this case there is a single base pair difference between the normal allele and mutated allele that enable expression of the non-functional or dysfunctional protein and development of a particular disease.

In the human body there are proteins called clotting factors that function to enable your body to respond to a wound and form a clot, preventing a dramatic loss of blood.  However, if one or more of the clotting factors are mutated, then your clotting system will not work properly.  This may result in reduced clotting as is seen in cases of hemophilia or too much clotting which occurs in the case of thrombosis or an increased tendency to from an abnormal blood clot in blood vessels.  Factor V is a clotting factor that when mutated leads to increased risk of thrombosis.  On such mutation that is associated with thrombosis both in its heterozygous and homozygous form is the factor V Leiden mutation (1691G>A)

Factor V Leiden thrombophilia is an inherited disorder of blood clotting that can lead to an increased risk of forming a type of clot that forms in the veins such as deep vein thrombosis. A person’s risk of developing a clot in a blood vessel depends on whether a person inherits one or two copies of the factor V Leiden mutation and the presence of other risk factors such as obesity, smoking and trauma. Inheriting one copy of the mutation increases an person’s risk of clotting by fourfold to eightfold. People who inherit two copies of the mutation, one from each parent, may have up to 80 times the usual risk of developing this type of blood clot. Considering that the risk of developing an abnormal blood clot averages about 1 in 1,000 people per year in the general population, the presence of one copy of the factor V Leiden mutation increases that risk to 4 to 8 in 1,000, and having two copies of the mutation may raise the risk as high as 80 in 1,000.

The factor V gene plays a critical role in the formation of blood clots in response to injury. The protein made by this gene, coagulation factor V, is involved in a cascade of chemical reactions enables blood clots to form and stick together. Another clotting protein called activated protein C (APC) prevents blood clots from growing too large by inactivating factor V. Individuals that have the factor V Leiden mutation, the APC moleculars are unable to inactivate factor V normally. As a result, the clotting process continues longer than usual, increasing the chance of developing abnormal blood clots.

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