Mitochondrial read fraction.
Barplot shows the fraction of total reads that map to the mitochondrial genome. This fraction can be influenced by sample type, cell viability, and nuclear permeabilization buffer. Mitochondrial read fraction > 0.3 should be discussed with Center staff. High mitochondrial read content reduces the fraction of total reads that are usable for downstream analysis, but does not necessarily mean that the remaining ATAC-seq reads are low quality.