I'm learning on my own how to perform differential expression of RNA-seq data from GEO (human cell lines). I selected a dataset that has a very weird CG content (see image above). Is this indicative of rRNA contamination? Is SortMeRNA adequate to remove rRNA contamination from these samples? FastQC also indicates the presence of overrepresented sequences (up to 0.4%) that BLAST to mtDNA. Could this be driving the GC content? Your help is appreciated! Thanks!