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Paternity Testing By Blood Type

Paternity Testing By Blood Type

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Paternity testing by blood type used to be the only way to establish paternity. Before the days of DNA testing, people used to look at blood type to determine if or if not a man could be the father of a child.  This was far from an exact science, but could narrow down the possibilities.  In the past, this typically involved identifying specific phenotypes (in particular, specific blood types) in the child and using this information to either “rule in” or “rule out” possible fathers. However, this system presented a number of problems, not the least of which was that it often yielded inconclusive results.

According to Wikipedia ” Blood types are inherited and represent contributions from both parents. A total of 35 human blood group systems are now recognized by the International Society of Blood Transfusion (ISBT).”   The main type of blood are A, B, O, AB, and the RhD factor, example A+ or B-.

Paternity Testing By Blood Type Today

Today, the best-known blood-typing system is ABO typing, which involves the presence of antigens on red blood cells that are encoded by the ABOlocus on human chromosome 9. In the ABO system, the A allele and the B allele are  codominate and the O allele is recessive. Thus, if a person’s ABO blood type is O, he or she has two O alleles. If, however, a person’s blood type is A, he or she has either two A alleles or one A allele and one O allele. Similarly, if a person has type B blood, this indicates the presence of either two B alleles or one B allele and one O allele. Finally, some people have type AB blood, which means they inherited both an A allele and a B allele. As you can determine, paternity testing by blood type isn’t specific enough for the accuracy needed.

From the website Dr. Geene.com http://www.drgreene.com/qa-articles/blood-types-102-role-ab-groups-determining-paternity/ is this chart with impossible situations for a child’s blood type. For example if the mother of your child had O blood and you have O blood and the baby has A, this would eliminate you from being the father of the child.

Using Blood Type in Determining Paternity:Possible and Impossible Situations

Parents’ Blood Types

Possible Children

Impossible Children

A & A

A, O

B, AB

A & B

A, B, AB, O

none

A & AB

A, B, AB

O

A & O

A, O

B, AB

B & B

B, O

A, AB

B & AB

A, B, AB

O

B & O

B, O

A, AB

AB &AB

A, B, AB

O

AB & O

A, B

AB, O

O & O

O

A, B, AB

 

These are general rules, though, and exceptions apply. Very rarely, gene mutations may change the rules such that “impossible children” become possible.

Today there are over 600 blood types known (as well as other tissue types called HLA types), which can make paternity testing far more accurate — but still not perfect.

DNA fingerprinting was developed by Alec Jeffreys in 1984, and it first became available for paternity testing in 1988.  Modern day DNA testing is 99.99% accurate, 999 out of 1000 accurate.  DNA testing is the standard legal test accepted today and is much more accurate that blood test used to be.

Paternity testing by blood type played it’s part in paternity history but check our other articles about DNA testing.