Given two multi-cellular species with obviously different phenotypes. The reason for the different phenotypes reflects their different DNA.

However two types of cells in an adult organism may have clearly different phenotypes (e.g. morphology), but the same DNA, with a different set of genes expressed.

To explain this it would seem that there must be some molecules to modulate the expression of the DNA in different cell types. In my reading I have found one such type of molecules the presence of which is prerequisite for one type of differentiation – modification of histons – methyl, phosphate, acetyl, ubiquitin. Another class of molecules is the transcription factors.

My question:

What would one look at to tell the differentiated type of a cell (ignoring its phenotype)?

Addendum: After having delved a little bit deeper into the topic of epigenetics, I'd like to suggest as a possible answer: it's the histone code one has to look at, something like: how the DNA is wrapped around which sequence (!) of (modified) histones.

  • $\begingroup$ I read the question a few times but I can't understand it. What do you mean by a species [.] in the sense of Darwin? What do you mean by a species of differentiated cells? $\endgroup$ – Remi.b Nov 8 '17 at 8:01
  • $\begingroup$ The two following two posts will likely help you. Why is a heritability coefficient not an index of how “genetic” something is? will tell you about what causes phenotypic variation (environmental variance, genetic variance, epigenetic variance, .... and all covariances). $\endgroup$ – Remi.b Nov 8 '17 at 8:04
  • $\begingroup$ How could humans have interbred with Neanderthals if we're a different species? will teach you about the difficulties and subtilities behind the concept of species. $\endgroup$ – Remi.b Nov 8 '17 at 8:04
  • $\begingroup$ @Remi.b: Thanks a lot for having tried to understand my question. I've got to admit that I obviously didn't manage to make clear what I mean. Possibly it's not even clear to myself? Another try: "Individuals of the same species share considerable portions of their DNA (next to having the same phenotype). What do individual cells in the human body of the same cell type have in common (next to having the same phenotype as cells) but not with other cells in the same body?" $\endgroup$ – Hans-Peter Stricker Nov 8 '17 at 10:09
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    $\begingroup$ This question may seem unclear, because of the non-biological background of the poster and the misuse of "species" in relation to cells. However, it is actually a very basic and important question. Put simply to a modern biologist one could say "If muscle cells and liver cells have the same DNA, what causes them to have a different morphology, i.e. what causes them to express different genes from the DNA?" The question hints at some of the reasons in mentioning modification of histones. The problem with answering the question is that it is very broad, and there is a lot we don't know. $\endgroup$ – David Nov 8 '17 at 13:25

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