Hi Harold, Thanks for your answer, but I'm not sure it is present in every header. Below the output of samtools view for one of our samples:
samtools view -H Part23_sampleA.bam
@HD VN:1.4 SO:coordinate
@PG ID:Isis PN:Isis VN:2.5.1.3
@SQ SN:M LN:16571 M5:6b9e15a5937653b0006de435f91578c0
@SQ SN:1 LN:249250621 M5:94f0d1b1622299238a1d8a0711dd06c7
@SQ SN:2 LN:243199373 M5:854e985b2e19c122b9f67f6453965693
@SQ SN:3 LN:198022430 M5:8abc85e73b1c75518a03743de2c2b14b
@SQ SN:4 LN:191154276 M5:2d37b4e662928cc6c58b84b2a4cc8648
@SQ SN:5 LN:180915260 M5:250f4e82a213269b0a0e4aebb0468470
@SQ SN:6 LN:171115067 M5:409088215d77f0bc72364b390430a5a7
@SQ SN:7 LN:159138663 M5:ef15cde5c82fb860694bf8f611807459
@SQ SN:8 LN:146364022 M5:8fbef8c3eaaac674cc6e690d1641464b
@SQ SN:9 LN:141213431 M5:791586215804a0eac537f38b9dd4cde2
@SQ SN:10 LN:135534747 M5:b4e45e54aa2f74160a3220c8f8e30a9a
@SQ SN:11 LN:135006516 M5:87a76a8bbb98a65b792822b8f148f4f9
@SQ SN:12 LN:133851895 M5:98b7a0aeea30cc16aeb5ffdaf43c8238
@SQ SN:13 LN:115169878 M5:90a7175dfa4e9c6d23fb0ec7b1f1e880
@SQ SN:14 LN:107349540 M5:98de20ecb80c00338fe4f978b0403d2b
@SQ SN:15 LN:102531392 M5:93273e983c0e06a2ec1334454952141e
@SQ SN:16 LN:90354753 M5:d252447e0439735eac934a27e9db136f
@SQ SN:17 LN:81195210 M5:ec9adf628757584300c3fb1a236a1c33
@SQ SN:18 LN:78077248 M5:1021a29f6559ff7d70a5e363f5b1daea
@SQ SN:19 LN:59128983 M5:74894b6505db2249cebf5f4b76a2f066
@SQ SN:20 LN:63025520 M5:c3c66d396289fe70950f844868c387df
@SQ SN:21 LN:48129895 M5:3e594b3726ece31187c113dd4ac85aa8
@SQ SN:22 LN:51304566 M5:9ba0d41360be59a22a837b7690cc80ac
@SQ SN:X LN:155270560 M5:e6c43bd374da923944dea2d6e0e6049b
@SQ SN:Y LN:59373566 M5:17ceeafc3a372967496cd94f2572c341
@RG ID:NGSA_A PL:ILLUMINA SM:NGSA_A
This doesn't allow to find the reference sequence that was used, or am I wrong?