In my qPCR experiments comparing gene expression between diseased and normal cells, I initially observed similar Ct values across two biological replicates. However, in the third replicate, the Ct value in diseased cells was approximately half (indicating much higher expression). I repeated the experiment with three new biological replicates, and consistently saw higher expression in the diseased cells across all three. How should I interpret the initial variation, and could this be due to biological variability, technical error, or sample quality differences?