How do prenatal paternity tests using SNP markers work?

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Is there any chance a NIPP (non-invasive prenatal paternity test) could yield a false negative result due to some factors (like paternal sample taken was of nails as opposed to the usual cheek swab; mother also has history of miscarriage 2.5 months prior to conception)? NIPP was done at 23 weeks.

I’m just confused as to how they came up with <0.000001% probability when the mismatches (correspond markers) are 300 out of the 1071 tested SNP markers. I’m confused as to how they came up with the results. Does this mean 300 markers didn’t match with the alleged father while the rest out of 1071 matched?

In: Biology

2 Answers

Anonymous 0 Comments

Why did you take nails as the dna?!? It’s not cells. It’s doesn’t really have the chromosomes. It’s keratin sheets.

It’s like hair. Hair also doesn’t really have dna. But hair follicles do.
Honestly I think there is a change the dna measured was contamination dna rather than like the dna of the potential father.

Anonymous 0 Comments

1. You don’t need all 1071 compared. If you have 300 as a sample size you are confident you have a good read on, you have plenty to give you extreme confidence whether there is parental relationship or not–this is not a cup of water to test the ocean case, this is a sampling 1/4 the cake to decide if it’s a vanilla cake or not case.

2. SNPs are Single Nucleotide Polymorphisms. Basically, numerous locations throughout your code that vary, and act as a genetic fingerprint for each individual. These are often a unique combination, even among identical twins, but there will still be similarities between family members especially when they are parental or offspring relationships.

3. Related to this: you should have something like 47% of each of your parents’ combination of SNPs, to a total of ~90% between the two of them, and ~50% in common with your siblings. Unless they are purposely cherry picking mismatched SNP locations *after* having conclusive results on at least ~600, there’s almost no way there’s parental connection. If they took 300 randomly, or 300 of the “we are sure these are the most clearly sequenced”, you would see many *many* matches if the other person was the parent.