Null Alleles are a rare exception found in results from yDNA STR testing. Often appears as 0* in FTDNA STR reports. Basically a condition where the test cannot measure the STR due to an SNP change in the primer OR, more rarely, where a complete segment of DNA has been removed. In either case, a value cannot be determined using the traditional CE technique for STRs from FTDNA and others.
Null Alleles need to be specially handled in genetic distance calculations. But, unfortunately, often are not. Worse case, they should be ignored or treated as a universal match. Treating them as a mathematical zero in the same sense as any other measured value is a mistake. But unfortunately how they are dealt with in the FTDNA genetic distance calculation for determining STR matches. Often a Null Allele STR value can be accurately determined through another test technique not using the normal primer ((NGS for example).
STRs in palindromic regions of the yDNA are often susceptible to changes in this manner.
Null Alleles need to be specially handled in genetic distance calculations. But, unfortunately, often are not. Worse case, they should be ignored or treated as a universal match. Treating them as a mathematical zero in the same sense as any other measured value is a mistake. But unfortunately how they are dealt with in the FTDNA genetic distance calculation for determining STR matches. Often a Null Allele STR value can be accurately determined through another test technique not using the normal primer ((NGS for example).
STRs in palindromic regions of the yDNA are often susceptible to changes in this manner.
External References
- Thomas Krahn's Null Alleles presentation at the 2009 FTDNA conference
- ISOGG Wiki Null Value page
- Thomas Krahn's Palindromic Regions presentation at the 2006 FTDNA 2006 conference (includes the yq11 Palindromic Region chart, version 2).
- Thomas Krahn's RecLOH description from the dna-fingerprints site (archived)
- Thomas Krahn's Walk The Y 2010 presentation from the FTDNA conference (slide 6 has an updated version 3 of the yq11 palindrome regions chart) (2012 repeat presentation with updates is also available)
- Elise Friedman of Relative Roots presentation on Advanced Topics on Y-DNA from FTDNA