On Monday, for the second time in as many business days, Illumina (ILMN -5.47%) stock took it on the chin because of an analyst recommendation downgrade. The biotech's shares closed the day almost 6% lower, during a session when the S&P 500 (^GSPC 0.67%) landed in the black with a 0.7% increase.The move is to sell now, says bankThat morning, Barclays changed its recommendation on Illumina stock to underweight (read: sell) from the previous equal weight (hold). It also pulled the lever on a significant price ...