Repetitive genomic sequences are challenging to sequence and assemble, creating difficult-to-analyze regions.

“there's certain regions of the genome that are complicated they're they're what we call repetitive sequences and so they may not be unique and it may be hard to even sequence through those regions and so putting those pieces back together in the right order um in some cases has been challenging to do and so sometimes you'll hear some of us as geneticist say there's a dark matter or there's some cryptic regions of the genome that we haven't been able to really dig into and that's because of some of these complexities of the sequences there and our ability to sequence through them”