I also just experienced the same thing with my DNA sequences, there are w's, Y', R', s' and k'. This is the very first time I've seen this. I am used to N but not these ones. Please kindly assist with knowing what might have caused these. Thanks in advance.
These are the so called "DNA ambiguity codes", when the sequencing result allows to bases at the position but it cannot be decided which. This can happen for example when you sequence genomic DNA and you have two different alleles present.
The code is the following (taken from this website):