[Bioforum] GRChr37: NN..NNACGTNN...NN

[Serikzhan S. Kazi]

Hi all,

if you inspect 
ftp://ftp.1000genomes.ebi.ac.uk/vol1/ftp/technical/reference/human_g1k_v37.fasta.gz 
--
the build "1000GP" used in their VCF results as a reference genome,
you'll find that every chromosome starts with a run of "N"s and ends 
with a run of "N"s.
The question is: how do they know what is the length of the chromosome 
in the first place
to put specific number of leading and trailing "N"s?