IBB tracks the Nasdaq Biotechnology Index, which includes biotechnology and pharmaceutical companies, including a 1.5% tilt toward ALKS.

FBT follows the NYSE Arca Biotechnology Index, which is equally weights biotech components. ALKS makes up 3.2% of the ETF’s holdings.

BBH tries to reflect the performance of the Market Vectors U.S. Listed Biotech 25 Index, which includes the largest biotech names. The fund has a 2.4% position in ALKS.

iShares Nasdaq Biotechnology ETF

Max Chen contributed to this article.