Since D21S11 is a complex repeat, allele designation is more problematic
than for simple repeats. Each allele in the D21S11 system has characteristics
of di-, tri-, tetra-, and hexanucleotide repeats. Two major systems of
nomenclature exist for D21S11.
Urquhart, et al.(str_ref 5) decided to name the alleles by the number
of TV dinucleotide repeats rather than naming alleles by length in base
pairs or using an arbitrary naming system. This method was chosen because
"it was consistent with nomenclature at the other loci in this system."
Since D21S11 is highly variable, "V" is used as a symbol to denote A, C,
or G. The variable sequence for this locus consists largely of TCTA and
TCTG repeats, but an invariant TA dinucleotide repeat and an invariant
TCA trinucleotide repeat also exist. Admittedly, there are two inconsistencies.
This nomenclature excludes the invariant TCA trinucleotide, and treats
the CA in the center of the TCCATA as a TV dinucleotide (See sequence information
for D21S11 in JPEG or
PDF
formats).
Moller, et al. (str_ref 34) named D21S11 alleles by their repeat number.
When the allele does not align with the ladder, digits after the decimal
point are used to indicate the number of basepairs by which the allele
exceeded the previous rung of the ladder.
