Y-STR and The Unsolved Murder of JonBenet Ramsey

A Y-STR is a short tandem repeat (STR) on the Y-chromosome. Y-STRs are often used in forensics, paternity, and genealogical DNA testing. Y-STRs are taken specifically from the male Y chromosome. These Y-STRs provide a weaker analysis than autosomal STRs because the Y chromosome is only found in males, which are only passed down by the father, making the Y chromosome in any paternal line practically identical.

STRs and forensics

In the United States, 13 different autosomal STR loci are used as a basis of analysis for forensic purposes. If crime scene DNA is ample and all 13 autosomal loci accessible, the likelihood of two unrelated people matching the same sample is around one in one billion.[5]

The basis for the profile probability estimation for Y-STR analysis is the counting method.[6] The application of a confidence interval accounts for database size and sampling variation. The Y haplotype frequency (p) is calculated using the p = x/N formula, where x is equal to the number of times the haplotype is observed in a database containing N number of haplotypes. For example, if a haplotype has been observed twice in a database of N = 2000, the frequency of that haplotype will be: 2/2000 = 0.001. Reporting a Y haplotype frequency, without a confidence interval, is acceptable but only provides a factual statement regarding observations of a Y haplotype in the database. An upper confidence limit for the probability of the Y haplotype in the population should be calculated using the method described by Clopper and Pearson (1934).[7] This uses the binomial distribution for the probabilities of counts, including zero or other small numbers that are found for Y haplotypes.

In genetic genealogy, Ysearch used to be the last sponsored database containing publicly submitted surnames and Y-STR haplotypes until its decommission on May 24, 2018, preceding by a day the implementation of the General Data Protection Regulation in the European Union, following a prolonged period of lacking support from its creator, Family Tree DNA. The database was founded in 2003 and reached 219 thousand records (among which 152 thousand unique haplotypes) before its shutdown. Other similar databases had disappeared earlier.[8][9]

Haplogroup (Y-SNP) specific data:

However, the same DNA from the underwear was found elsewhere around the body. It was under the fingernails, under the waistband of the victim's leggings, on the wrist bindings and on the garrote.