1.看文献，bowtie2比对ChIP-seq数据，The multimapped reads were kept for TE analysis, but only the best alignment was reported for those reads; if more than one equivalent best alignment was found, then one random alignment was reported.这里说的如果多于1个best的时候，随机选一个，应该怎么设置呢，bowtie2的default可以实现这个功能吗？
2.对于双端测序，bowtie2比对的aligned concordantly的reads，跟samtools flagstats里报告的properly paired reads，是一个意思吗？
