A systematic analysis of the most commonly amplified 18S rRNA hypervariable regions and the effect that PCR/sequencing bias has on community representation. The V4 and V8-V9 hypervariable regions were amplified for seven mock communities and for freshwater, marine, and wastewater samples to compare the sequenced community structure to theoretical communities and validate these results with environmental samples. This project contains mothur script files for analyzing the data.