Earlier this month, the PowerShares Dynamic Biotechnology & Genome Portfolio (NYSEArca: PBE) and the SPDR S&P Biotech ETF (NYSEArca: XBI) soared because the two ETFs feature the largest weights among biotech funds to Idenix Pharmaceuticals (NasdaqGS: IDIX), which tripled in a day after news Merck (NYSE: MRK) will acquire the company. [Why These Biotech ETFs are Soaring]

In January, XBI surged more than 7% in one day after shares of Intercept Pharmaceuticals (NasdaqGM: ICPT) nearly quadrupled after trials for the company’s liver disease treatment proved successful. [Intercept Lifts This Biotech ETF]

The day those trial results were released, Intercept occupied just 1.6% of XBI’s weight.

First Trust NYSE Arca Biotechnology Index Fund