Explore Evolution insists, contrary to the consensus of developmental biologists, that we don't really know what controls development or whether that mystery force could mutate:

Some developmental biologists now think that two other cellular features – the cytoskeleton and the cell membrane – store structural information that affecdts how the embryo develops, but there is much we do not know yet.

What we do know is that if DNA doesn't control development, something else must. Identifying the "something else" is one of the next great areas of research. Another question, of course, is whether the "something else" can be altered by mutation, which would provide a whole new vista of variations on which natural selection could act. Is this what research will reveal? Or will it reveal even deeper questions? Stay tuned.

Explore Evolution, p. 111

Explore Evolution is not clear whom they are referring to in this passage. If this is truly "the next great area of research," an "inquiry-based" textbook would do well to lead students through the leading hypotheses and the evidence researchers in the field are considering, so that students could engage in their own inquiry. Unfortunately, the citations offered earlier in this chapter are uninformative. Franklin Harold, cited earlier and quoted in this critique observing that "[s]patial organization … emerges from the interplay of genetically specified molecules," takes this position:

I do not mean to imply that eukaryotic cells are the product of intelligent purposeful design, the supposition is that the adaptive evolution of a cytoskeleton and intracellular membranes made possible the proliferation of larger cells displaying varied and elaborate morphologies.

Franklin Harold (2001) The Way of the Cell, p. 121

Another possibility is the creationist pseudoscience of Jonathan Wells:

Jonathan Wells, a molecular biologist with the Discovery Institute, argues that genes, environment, and cell structure all affect development. DNA controls the production of proteins that affect development, but the cytoskeleton (a network of microscopic fibers) and certain features in the cell membrane determine what happens to these proteins after they are made…

"The notion that genes control development is a fallout from neo–Darwinian evolutionary theory," Mr. Wells added. Evolutionists use genetic mutations to explain how organisms could change gradually over time. But if development involves the entire egg, then its complexity is much stronger evidence that a Creator designed life.

L. Sillars (2000) Cracking the Code, World Magazine

Setting aside the absurd implication that evolutionary biologists think that development does not involve the "entire egg," could genes affect how the egg is produced? Indeed they can and do. Fruit fly geneticists have searched for "maternal effect mutations" in such genes and have identified genes necessary for the proper construction of the oocyte, the future egg. One such gene encodes Protein Kinase A (PKA) that has a direct effect upon the organization of microtubules through mediating a external signal from nearby follicle cells.

Microtubule polarity has been implicated as the basis for polarized localization of morphogenetic determinants that specify the anteroposterior axis in Drosophila oocytes. We describe mutation affecting Protein Kinase A (PKA) that act in the germ line to disrupt both microtubule distribution and RNA localization along this axis.

M. E. Lane and D. Kalderon (1994) "RNA localization along the anteroposterior axis of the Drosophila oocyte requires PKA-mediated signal transduction to direct normal microtubule organization," Genes and Development 8, p. 2896

Unfortunately for creationists, the organization of microtubules in the oocyte is under genetic control and will be sensitive to mutation. In this case, a mutation affecting PKA function in the egg can result in an embryo which has heads at both ends, or in more subtle variations. In a similar fashion, if the "certain features of the cell membrane" are due to actions of proteins, either in the cell membrane or involved in generating the cell membrane of eggs, they will also sensitive to genetic control and mutation, since, as Harold observes, those structures are genetically specified.