You might like to think about the way in which imagery is so strongly linked to the various allusions in the novel, especially the way that the text is connected so strongly to Greek mythology. This is particularly relevant of course in the presentation of the character of Cal, and also these allusions develop a number of symbols.
For example, consider the way in which Cal reads Tiresias in the play of Antigone that her school present. There is an obvious parallel between Cal and Tiresias, as both were "one thing and then the other" in terms of the way that both characters change gender and also are prophets. It is clear too that obvious reference is made to Homeric poetry in Cal's deliberate imitation of the Homeric form. Consider this deliberate pastiche of Homer:
Sing now, O Muse, of the recessive mutation on my fifth chromosome! Sing how it bloomed two and a half centuries ago on the slopes of Mount Olympus, while the goats bleated and the olives dropped.
This is an excellent example of imagery in the novel, but it also is important in the way that it demonstrates how Cal views herself as being connected to Greek mythology.