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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.

canadianer
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Hans-Peter Stricker
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  • 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? – Remi.b Nov 08 '17 at 08:01
  • 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). – Remi.b Nov 08 '17 at 08:04
  • 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. – Remi.b Nov 08 '17 at 08:04
  • @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?" – Hans-Peter Stricker Nov 08 '17 at 10:09
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    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. – David Nov 08 '17 at 13:25
  • @David: I understand, "species" is not to be used related to cells. But I'm quite sure to have heard of "populations of cells". Is "cell type" an acceptable term for "species of cells"? – Hans-Peter Stricker Nov 08 '17 at 13:30
  • I have modified and simplified your question in an attempt to focus it and prevent it being removed as unclear. Yes "cell type" is the term used. If you don't like my changes you can revert them. The problem now is that you have (partly) answered the question yourself. Unless someone (not me) has a reference to a good review or can write a good thumbnail account, I'm not sure where we can go from here. – David Nov 08 '17 at 13:39
  • You saw that part in your wiki link that the "histone code" is just a hypothesis? The development of the anterior-posterior axis in fruit flies is pretty well explained with RNA gradients, and not so much histone positioning. Here's a hint, RNA seq is a much more common application than CHiPseq on histones. – swbarnes2 Nov 09 '17 at 00:00
  • @swbarnes2: I did. RNA seq and CHiPseq seem to be hard stuff for the novice. – Hans-Peter Stricker Nov 09 '17 at 09:04
  • Well, you are not asking a question that can be answered by a novice in biology, either. Scientists asking "How are these tissues different" are generally not starting with CHipSeq; they do RNAseq, or 10 years ago, microarrays. – swbarnes2 Nov 09 '17 at 18:04

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