wget http://hgdownload.cse.ucsc.edu/goldenPath/hg19/chromosomes/chrX.fa.gz;

wget http://hgdownload.cse.ucsc.edu/goldenPath/hg19/chromosomes/chrY.fa.gz;

152M Mar 21  2009 chrX.fa

58M Mar 21  2009 chrY.fa

然后把X染色体构建bwa的索引

bwa index chrX.fa

[bwa_index] Pack FASTA... 1.97 sec

[bwa_index] Construct BWT for the packed sequence...

[BWTIncCreate] textLength=310541120, availableWord=33850812

[BWTIncConstructFromPacked] 10 iterations done. 55838672 characters processed.

[BWTIncConstructFromPacked] 20 iterations done. 103157920 characters processed.

[BWTIncConstructFromPacked] 30 iterations done. 145211344 characters processed.

[BWTIncConstructFromPacked] 40 iterations done. 182584528 characters processed.

[BWTIncConstructFromPacked] 50 iterations done. 215797872 characters processed.

[BWTIncConstructFromPacked] 60 iterations done. 245313968 characters processed.

[BWTIncConstructFromPacked] 70 iterations done. 271543920 characters processed.

[BWTIncConstructFromPacked] 80 iterations done. 294853104 characters processed.

[bwt_gen] Finished constructing BWT in 88 iterations.

[bwa_index] 98.58 seconds elapse.

[bwa_index] Update BWT... 0.96 sec

[bwa_index] Pack forward-only FASTA... 0.91 sec

[bwa_index] Construct SA from BWT and Occ... 33.18 sec

[main] Version: 0.7.8-r455

[main] CMD: /lrlhps/apps/bioinfo/bwa/bwa-0.7.8/bwa index chrX.fa

[main] Real time: 141.623 sec; CPU: 135.605 sec

由于X染色体也就152M，所以很快，两分钟解决战斗！

然后模拟Y染色体的测序判断（PE100，insert400）

209M Oct 28 10:19 read1.fa

209M Oct 28 10:19 read2.fa

模拟的程序很简单

while(<>){
chomp;
$chrY.=uc $_;
}
$j=0;
open FH_L,">read1.fa";
open FH_R,">read2.fa";
foreach (1..4){
for ($i=600;$i<(length($chrY)-600);$i = $i+50+int(rand(10))){
$up = substr($chrY,$i,100);
$down=substr($chrY,$i+400,100);
next unless $up=~/[ATCG]/;
next unless $down=~/[ATCG]/;
$down=reverse $down;
$down=~tr/ATCG/TAGC/;
$j++;
print FH_L ">read_$j/1\n";
print FH_L "$up\n";
print FH_R ">read_$j/2\n";
print FH_R "$down\n";
}
}
close FH_L;
close FH_R;

然后用bwa mem 来比对

bwa mem -t 12 -M chrX.fa read*.fa >read.sam

用了12个线层，所以也非常快

[main] Version: 0.7.8-r455

[main] CMD: /apps/bioinfo/bwa/bwa-0.7.8/bwa mem -t 12 -M chrX.fa read1.fa read2.fa

[main] Real time: 136.641 sec; CPU: 1525.360 sec

643M Oct 28 10:24 read.sam

然后统计比对结果

samtools view -bS read.sam >read.bam

158M Oct 28 10:26 read.bam

samtools flagstat read.bam

3801483 + 0 in total (QC-passed reads + QC-failed reads)

0 + 0 duplicates

2153410 + 0 mapped (56.65%:-nan%)

3801483 + 0 paired in sequencing

1900666 + 0 read1

1900817 + 0 read2

645876 + 0 properly paired (16.99%:-nan%)

1780930 + 0 with itself and mate mapped

372480 + 0 singletons (9.80%:-nan%)

0 + 0 with mate mapped to a different chr

0 + 0 with mate mapped to a different chr (mapQ>=5)

我自己看sam文件也发现真的同源性好高呀，总共就模拟了380万reads，就有120万是百分百比对上了。

所以对女性个体来说，测序判断比对到Y染色体是再正常不过的了。如果要判断性别，必须要找那些X,Y差异性区段