Masked genomes/sequence refer to genomic sequence that has been scanned for some type of internal sequence and then has those sequences converted to "X". Usually, repeat sequences are identified and masked as these cause sequence comparison algorithms to spend a lot of time identifying and matching these sequences
由于将重复序列放入comparison 中会导致program运行时间过长，所以将这些repeat sequence识别出来然后mask掉：如图：
