The first cleavage of the mouse zygote predicts the blastocyst axis:
One of the unanswered questions in mammalian development is how the embryonic–abembryonic axis of the blastocyst is first established. It is possible that the first cleavage division contributes to this process, because in most mouse embryos the progeny of one two-cell blastomere primarily populate the embryonic part of the blastocyst and the progeny of its sister populate the abembryonic part.
By looking at a mouse, we generate a testable hypothesis about all mammals, and maybe all deuterostomes: They should all work the same way. This research matters because of common descent.