What are "HET" regions in a genome?

Question

[alanh]

I was looking at a couple of the metadata files describing the regions of GRCh38 (e.g. centromeres, alternate scaffolds, etc.), and one of the lines is the following:

HET7 7 61377789 61528020 HET na na na

This is the only "HET" region in the human genome, and I can't find any details documenting this anywhere in Google, I checked the Genome Browser and there isn't any special indication about the region, and I asked some knowledgable colleagues and they didn't know either.

[h.mon]

Where are these metadata files from? Which is the file in question?

[alanh]

From https://www.ncbi.nlm.nih.gov/assembly/GCA_000001405.28

clicked on "Download the regions report" on the upper right, which yields this URL:

ftp://ftp.ncbi.nlm.nih.gov/genomes/all/GCA/000/001/405/GCA_000001405.28_GRCh38.p13/GCA_000001405.28_GRCh38.p13_assembly_regions.txt

It's line 212 in that file.

Answer 1

[h.mon]

Apparently it is an heterochromatic region. It is listed at the table Modeled centromeres and heterochromatin regions found at the Genome Reference Consortium Human Genome Overview page. It doesn't have an "assembly unit", probably because it is composed of repetitive material and thus currently impossible to assemble.