Source:
- Episode 11 of The Killing of JonBenet podcast and also from a podcast that I don’t remember the name, but Mitch Morrisey was a guest on the episode.
- I have a degree in biochemistry and cell biology and genetics was part of the curriculum.
So, I’ll see if I can explain better, because I re read my prior post and it is confusing (and has an error).
So, CODIS stores information from samples from 20 core DNA loci and these 20 core loci are “autosomal loci” meaning that BOTH the “X” chromosome and “Y” chromosome have the same gene (but, that gene has a particular DNA “code” or allele). So, when those two alleles from an individual are put together, then they form their own “Code” let’s say A145a273 for an example. So, because the larger DNA sample that we have from JBR is mixed with her blood, and at least one other “X” chromosome from another individual, then we can’t reliably tell what “X” chromosome belongs to the offender. So, the partial Y- STR profile that is available from the offender hasn’t yielded any matches because the FBI uses a stringent search criteria that considers a “match” when there is a 1 in 10 million probability that it belong to one person. So, thinking of it backwards… when the DNA is run in CODIS, it’s actually encountering too many “matches” to the point that it can’t give a good probability. (That’s my understanding at least). So, JAR and investigative team in the podcast interviewed a world-renowned forensic scientist from the UK to discuss how, in other countries, they lower the parameters, so that they can at least get some results (like, lower it to a probability of say 1 in 1 million). I hope that makes sense?
Edited to fix error