Digital Biology Friday: A DNA sequencing data puzzle

I know some of you enjoy looking at data and seeing if you can figure out what's going on.

For this Friday's puzzler, I'm going to send you to FinchTalk, our company blog, to take a look at lots of data from a resequencing experiment that was done to look for SNPs and count alleles. The graph is at the end of the post.

The graph shows data from 4608 reads (sequenced from both strands, forward and reverse). And there are some interesting patterns. Can you figure them out?

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