[ensembl-dev] unambiguity code

[Sung Gong]

Hi,

In Bio::EnsEMBL::Variation::Utils::Sequence, it reads:

my %unambig = qw(M AC V ACG N ACGT H ACT R AG D AGT W AT S CG B CGT Y
CT K GT C CC A AA T TT G GG - --);

Any reason for AA, TT, GG, CC for A, T, G and C, respectively?
Maybe easier for just a single letter?

Cheers,
Sung