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Showing content from https://github.com/lh3/minimap2/issues/816 below:

Missing 1 Mbp of alignment on Chromosome 16 between T2T-CHM13 v1.0 and GRCh38 · Issue #816 · lh3/minimap2 · GitHub

Hi Heng,

I am looking at a 1 Mbp region on chr16 that doesn't seem to align when comparing GRCh38 and T2T, but there is a lot of homology in the region. When I do a whole genome alignment I get about 1 Mbp of missing alignment around ~chr16:21,000,000-22,000,000 and more specifically I get these alignments (including the flanking regions):

chr16   90338345        15116377        21305673        +       chr16   96330493        15117341        21337915
chr16   90338345        21430746        21466480        +       chr16   96330493        21709065        21744757
chr16   90338345        22472332        28471794        +       chr16   96330493        22750307        28752414

With this command (version 2.22):

minimap2 \
            -cx asm20 --eqx --secondary=no \
            -s 10000 -t 100 -K 8G \
            ../assemblies/chm13.draft_v1.0.fasta ../assemblies/hg38.chr_only.fa 

And here is an image of the alignment (T2T on the bottom)

However if I take just the region that is mostly unaligned and align it then I get a nearly complete alignment in the reverse complement, suggesting a missed inversion I think.

chr16:21305673-22472332 1166660 160939  1166660 -       chr16:21337915-22750307 1412393 406974  1412393 1005059
chr16:21305673-22472332 1166660 91920   196680  +       chr16:21337915-22750307 1412393 337923  442372  103880  105150

Command:

minimap2 \
  -cx asm20 --eqx --secondary=no \
  -s 10000 -t 100 -K 8G \
  <(samtools faidx ../assemblies/chm13.draft_v1.0.fasta chr16:21337915-22750307 ) \
  <(samtools faidx ../assemblies/hg38.chr_only.fa chr16:21305673-22472332 )  \

I have also dropped the two paf files and references at this link:
https://eichlerlab.gs.washington.edu/help/mvollger/share/mm2-issue-chr16/

I am not sure the cause of this, but it seems like a large event to miss, and hopefully I this is not just some mistake on my part.

(And credit to Ariel Gershman for finding this issue, if it is a real issue and not some mistake on my part)

Thanks in advance!
Mitchell


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