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Null value

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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

Haplogroup

(Longhand)

Haplogroup

(Shorthand)

Marker Project Name Administrator(s) Members Status
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

See also

Further reading