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In next generation sequencing, DNA is amplified and then processed into relatively short DNA fragments, called "reads," which are sequenced and then mapped to their position in the genome computationally. An important variable in next-generation sequencing is the "coverage" of each site in the genome, which means the number of times that fragments containing the site were sequenced, i.e., the number of reads covering the site. In a diploid organism, like humans, there are two distinct copies of each site in the autosome (i.e., nuclear DNA not counting the sex chromosomes), one maternal copy and one paternal copy. Assume that if a read covers a site, it has a 50% chance of being the maternal copy and a 50% chance of being the paternal copy, independently of all other reads covering the site. The figure below illustrates these ideas. The vertical black line represents a particular site in the genome. The horizontal lines represent reads that cover this site: the horizontal blue lines represent reads from the paternal chromosome, and the horizontal red lines represent reads from the maternal chromosome. So for the example in the figure, there are 5 reads that cover the site, 3 reads are from the paternal chromosome, and 2 reads are from the maternal chromosome.