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In late October 2008, the L21 SNP was discovered under P312. A month later, L21 was added to ISOGG's R clade of the Human Phylogenetic Tree. In early October 2009, L69 was discovered under L21 within the "Walk Through the Y" project.
The L69/L159 polymorphism is essentially a SNP/STR oxymoron. The base change happens right at the intersection of a poly G homopolymer and a GT dinucleotide repeat. In the case of L69+ the poly G is shortened from 6 to 4 bases and the dinucleotide repeat gains one unit. In the case of L159+ the poly G is elongated from 6 to 8 bases and the dinucleotide repeat loses one unit.
This alignment of sequences may make this clearer:
AAACTGGGGGGGGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGCG (L159+)
AAACTGGGGGGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGCG (HUGO and most others)
AAACTGGGGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGCG (L69+)
L69................^
L159...................^
(note that the GT repeat count may vary and is disregarded for the L69/L159 status)
The L69/L159 polymorphism is certainly not a UEP because it has been observed in various other haplogroups and we are certainly at the very beginning of understanding its mechanism and phylogenetic relevance. We have to be careful because it can "mutate" back like a regular STR. However with caution it may be a good help to sort out genealogies and haplotype clusters. Only further testing will answer the question how useful this polymorphism may be and what mutation frequency we can expect.
WHO CAN JOIN: Anyone who has received a positive result for L21 and L69 from FamilyTreeDNA.
The L69/L159 polymorphism is essentially a SNP/STR oxymoron. The base change happens right at the intersection of a poly G homopolymer and a GT dinucleotide repeat. In the case of L69+ the poly G is shortened from 6 to 4 bases and the dinucleotide repeat gains one unit. In the case of L159+ the poly G is elongated from 6 to 8 bases and the dinucleotide repeat loses one unit.
This alignment of sequences may make this clearer:
AAACTGGGGGGGGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGCG (L159+)
AAACTGGGGGGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGCG (HUGO and most others)
AAACTGGGGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGCG (L69+)
L69................^
L159...................^
(note that the GT repeat count may vary and is disregarded for the L69/L159 status)
The L69/L159 polymorphism is certainly not a UEP because it has been observed in various other haplogroups and we are certainly at the very beginning of understanding its mechanism and phylogenetic relevance. We have to be careful because it can "mutate" back like a regular STR. However with caution it may be a good help to sort out genealogies and haplotype clusters. Only further testing will answer the question how useful this polymorphism may be and what mutation frequency we can expect.
WHO CAN JOIN: Anyone who has received a positive result for L21 and L69 from FamilyTreeDNA.