Why is this? Is this something about the biotech sector, or because mutual funds incur more capital gains, or just a difference in strategy? (Maybe FBIOX is more actively managed vs. IBB, which just tracks an index)
Index funds, like IBB, generally lack active management, which equates to lower expenses. This is simply because the target index, the NASDAQ Biotechnology Index in the case of IBB, is composed of known quantities. This means there won't be stock pickers or analysts constantly swapping holdings, increasing the turnover rate of the portfolio and increasing capital gains; costs that are offset by higher expense ratios in more actively managed funds.