Chimerism

[Auricman]

On Monday night (Dec. 26) on the Discovery Health Channel I saw an interesting program which may call into question the absolute reliance the American courts have in DNA testing. It had been previously believed that if a parent has at least 50% of the DNA matching of a child, the parent was indeed the child's parent, and if there was not at least 50% matching, then the presumed parent was not actually the child's parent. But a woman in Massachusetts needed a kidney transplant and her children were tested to see if their DNA matched closely enough to donate their kidney to her. To everyone's surprise, her children's DNA did not match the mother's.

Another woman in Texas was suspected of welfare fraud because her DNA did not match her children's DNA.

Both these cases underwent extensive scrutiny for months, with DNA samples studied from not just the blood, but also samples from the internal organs. What the scientists found was that both women had two different DNA sets in their bodies. Their blood DNA did not match that of some of their internal organs. The women were unkowingly Chimers (from Chimerism), which means that early in the womb, two different embryos fused to form one fetus, resulting in two different sets of DNA in one person. The condition is believed to be rare, but unless a person has a reason to have the DNA tested, it may never be known that the person is a chimer.

What is the bottom line? If a suspect's blood DNA doesn't match that from the crime scene, the suspect could still be actually guilty if the other set of DNA does match but is not tested.

[MaiLuk]

Interesting post. So its possible that when a chimer man is tested for paternity, the test may come back negative even though he really is the father.

 

>>What is the bottom line? If a suspect's blood DNA doesn't match that from the crime scene, the suspect could still be actually guilty if the other set of DNA does match but is not tested.<<

 

I'm no expert but if the blood at the scene is his, it will definitely match the dna in his blood right? Can't have two different blood DNAs. But, if he left blood at the scene and they took a saliva sample from him, then the DNA may not match.

 

They say chimerism is rare but how do they know? Have they tested a population sample to determine its frequency? Doubt it. Maybe it occurs more than realized.

[Auricman]

I'm no expert but if the blood at the scene is his, it will definitely match the dna in his blood right? Can't have two different blood DNAs. But, if he left blood at the scene and they took a saliva sample from him, then the DNA may not match.

I believe what you say is correct. Also, in rape and paternity cases, the semen may match although the blood might not match.

web page describing Chimerism

BTW, the correct term for someone with chimerism is Chimera , not Chimer as I called it in the OP.