From ISOGG Wiki
A null value is the term used when a DNA laboratory is unable to determine a value for a short tandem repeat (STR) marker on the Y-chromosome. A null value may be caused by missing genetic material, or a single-nucleotide polymorphism (SNP) near the location of the marker. The SNP prevents a value from being detected. SNPs and nulls, like other marker variations, are passed down on the Y-chromosome from father to son. Null values are often characteristic of specific haplogroups or subclades, but can occur independently in many different haplogroups. For the purposes of calculating genetic distance a null is counted as a single-step mutation.
The ISOGG project administrators' mailing list maintains a database of null markers which can be found in the group's files section under databases. It is accessible from this link if you are logged into your Yahoo account.
The genetic genealogy pioneer Leo Little had a special interest in nulls and at the time of his death in 2008 was the leading authority on the subject within the genetic genealogy community.
Note that in late 2012 Family Tree DNA changed their reporting system following the move from the lab at the University of Arizona to their own Genomics Research Center in Houston, Texas. FTDNA now use a different primer for DYS439 and all results which were previously reported as nulls will now show as 12 repeats. The old null 439 project (see below) has now been renamed as the R1b-L1/S26 Y-DNA Haplogroup Project. New members of Haplogroup R-L1 will have their actual test results at DYS 439 which may or may not be 12 repeats. They will only know they are Haplogroup R-L1 by testing the L-1 SNP or by Geno 2.0 testing from the Genographic Project.
Null value projects
|All haplogroups||DYS425||Null425 Project||Tibor Fehér||300||Active|
|All haplogroups||DYS448||The NULL448 Project||15||Active|
|R1b1a2a1a1b3||R-L21||DYS425||Clan Colla 425 null project||Patrick McMahon, Peter Biggins||310||Active|
- A null primer ISOGG newsletter Vol. 1 No. 4 Jun/Jul 2008
- Thomas Krahns' presentation on null alleles from the Family Tree DNA conference in Houston, Texas in 2009 File size 8 mb
- Definition of a null FTDNA Learning Center
- How is genetic distance calculated for null values? FTDNA Learning Center
- Allele dropout/Null allele reports NIST article