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rs121908745(A;A)

From SNPedia

Common (in Ancestry reports); no need to worry
Is agenotype
ofrs121908745
GeneCFTR
Chromosome7
Position117,559,590
mentionedby
Magnitude0
ReputeGood
Geno Mag Summary
(-;ATC) 3 carrier of a cystic fibrosis allele
(A;A) 0 Common (in Ancestry reports); no need to worry
(ATC;ATC) 0 common in clinvar

The (A;A) genotype is the most commonly reported one for Ancestry users, so it's the common/normal form. However, in public databases, rs121908745 should be either "ATC" or "nothing", in other words, a deletion of the "ATC", so to report (A;A) as a possible genotype for this SNP is actually an error on Ancestry's part.