hg19 has new sequences: chrMT is the revised Cambridge Reference Sequence mitochondrion (NC_012920), as opposed to chrM (deprecated NC_001807). Patch sequences from GRCh37.p13 have also been added to hg19.
More information available here:
https://genome.ucsc.edu/goldenPath/newsarch.html#031720
Jairo Navarro
UCSC Genome Browser
UC Santa Cruz Genomics Institute
Revealing life’s code.
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