Directions: Select the most appropriate filler(s) for the blank(s) such that the sentence makes coherent sense.

It is a great ________ to be able to transfer useful genes with as little extra gene material as possible, because the donor's genome may contain, in addition to desirable genes, many genes with _______ effects.

'Little extra gene material' in the first part of the sentence provides the clue for the second. This implies that in addition to desirable genes, there are many genes with negative effects, so it will advantageous to transfer useful genes with as little extra gene material as possible. 'advantage' and 'deleterious' (harmful) in option (4) fits our prediction, hence the answer.