One mismatch rules a person out
- The idea
- Predict
- See it
- Why
- Check
The idea
“If most of the alleles agree, the two DNA profiles match.”
When nearly every number lines up, it looks like a match. A person's own DNA would line up at every one.
The short version
The mistake: If most of the alleles agree, the two DNA profiles match.
What's actually true: Two samples from one person agree at every locus, so a single clear mismatch rules that person out.
- An STR, or short tandem repeat, is a spot where a short DNA sequence repeats. People differ in the repeat count. You have two alleles at each locus, one from each parent.
- Your blood, skin and hair roots all carry the same DNA. A sample you left must agree with you at both alleles, at every locus.
- Sharing some alleles is common. Agreeing at every locus is rare, so a full match is strong evidence.
On the exam: Check both alleles at every locus. One clear mismatch rules a person out.