iShares Biotech Fund (IBB) came under pressure yesterday on concerns over legislation that could potentially hurt companies in the sector. IBB fell 3.4 percent in midday action. Today, however, biotech stocks are seeing relative strength after Roche finalized its bid for Genentech (DNA) and Gilead (GILD) said it was buying CV Therapeutics (CVTX) . The exchange-traded fund made up all Wednesday’s losses and more. IBB is up $3.10, or 5.2 percent, to $63.33 and trading is brisk in IBB April and June calls at the $70 strike.