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Explore Evolution asserts:

Something else – some other source of information – must orchestrate the assembly of the component proteins into unique cell types and direct the organization of cell types into various tissues and organs, and controls the arrangements of organs and body parts into an overall body plan (18).
Explore Evolution, p. 110

As to the nature of this "other source of information" that is not DNA, Explore Evolution cites a study in the history of science by Jan Sapp, Beyond the Gene: Cytoplasmic Inheritance and the Struggle for Authority in Genetics. In one section, Sapp describes how embryologists at the start of the 20th century thought the cytoplasm played the most prominent role in directing development and heredity. A more contemporary topic that Sapp examines is cortical inheritance in ciliates, single celled organisms such as paramecium. Ciliates divide by fission and the two daughter cells are able to inherit the pattern of cilia at their cell cortex. This inheritance of ciliary patterns is an example of cytoplasmic inheritance and appears to be largely independent of direct control by nuclear genes.

As Sapp noted in 1987,

Even some leading neo-Darwinian evolutionists have admitted their concern about the significance of the "the phenomenon of cortical inheritance in ciliates." At a symposium on Development and Evolution held at the University of Sussex in 1982, the centenary year of Darwin's death, John Maynard Smith (1983) p. 39) stated "Neo-Darwinists should not be allowed to forget these cases, because they constitute the only significant threat to our views."
Jan Sapp (1987) Beyond the Gene: Cytoplasmic Inheritance and the Struggle for Authority in Genetics, p. 219-220

However, to date, cortical inheritance has failed to displace nuclear genes as the most important player in regulating embryonic development in the ensuing 25 years after John Maynard Smith's warning to fellow evolutionists. Indeed, in this period there have been two sets of Nobel Prizes for scientists who have been leaders in the genetic analysis of animal development.

As Alessandro Milenni – also cited by Explore Evolution notes:

From the point of animal evo-devo, the question is whether these aspects of cytoplasmic information (cytotaxis sensu, Sonneborn, 1964) are limited to ciliates or are a general property of cells. I am not aware of the inheritance of intracellular patterns in animals, but it is certain that very few biologists have thought it a rewarding topic be investigated.
Alessandro Minelli (2003) The Growth of Animal Form, p. 29

Far from supporting the claim that modern biologists cytoplasmic factors as an alternative to DNA, the citations offered by Explore Evolution actually show that science has rejected various alternatives and all evidence points to DNA as the repository of "instructions" for biological development.