When performing quality control on FASTQ data, what specific statistical pattern in the base-call distribution indicates that the sequencing library contains adapter contamination?

When performing quality control on FASTQ data, adapter contamination is identified by a specific rise in the frequency of non-genomic sequences at the 3' end of the reads. FASTQ data consists of sequences of nucleotides, which are the building blocks of DNA represented by the letters A, T, C, and G, accompanied by quality scores. During sequencing, adapters are short, synthetic DNA molecules attached to the ends of ta....