Is it possible that on the same pileupcolumn object (i.e a specific aligned base) I find the same base but aligned to different strands? For example, can I find a coverage of 50 'A's that align to strand '+', and on the same time 50 'A's that align to strand '-' within the same index? I expect that if 'A' is aligned to strand '+', I will find 'T' aligned to strand '-'.
As @terdon mentions, it's certainly possible to have an
A aligned on both strands. If a read has a mismatch at the location of interest and that mismatch is the complement of the reference base, then you are likely to see
A in both strands. However, it is very unlikely you will see the same base at high coverage in both strands. For example, if your total coverage is 55, and you see 50
As on the + strand and 50
As on the - strand, it's likely that the pileup object is reporting the reverse complement sequence of the reads that align to the - strand for your convenience.