I have a (probably stupid) question about how the chromosome positions are numbered in SAM files.
I used bowtie to align reads to hg19 and got SAM files as output. I pulled the columns indicating chromosome and position so that I have files that look like:
chr, position
chr1, {starting position for read 1}
chr1, {starting position for read 2}
chr1, {starting position for read 3}
... etc.
My question is: do the position indices reset at each chromosome (i.e position 1 on chromosome 2 would read "chr2, 1") or does the position indicate the position within the entire genome (i.e. if chromosome 1 has X positions, position 1 on chromosome 2 would read "chr2, X+1")?