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Are there genes that are expressed in every cell in organism

  1. Oct 13, 2016 #1
    I know that different cells in a body express different genes and thus have different functionalities.

    I am wondering if there are genes that are expressed in all the cells of a certain organism. (or for that matter in all the cells that have that specific gene, for example all mammals.)?

    For example, maybe the gene that tells the cell to have a nucleus? Or some other function that is common to all the mammalian cells for example?

    Hope I'm on the right track with this question.
  2. jcsd
  3. Oct 13, 2016 #2

    Simon Bridge

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    Well, there are "certain organisms" that are single celled organisms. All their genes are expressed in every cell they possess.
    Is this a homework question?
  4. Oct 14, 2016 #3
    Thanks Simon. I actually had multicellular organisms in mind. And in particular, whether in a large organism, all cells have certain amount (a subset) of genes that are express in each cell, and the rest are the genes expressed for each cell's specific differentiated functionality.
    Not a homework question, just curiosity.
  5. Oct 14, 2016 #4

    Fervent Freyja

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    Most cells carry the organisms nuclear DNA, which is exactly the same, except for sperm cells and eggs. Some cells, like mature red blood or other non-nucleated cells do not carry DNA. That doesn't mean the entire genome will be utilized in that cell, there are other variables that determine how it is used.

    Have you tried any online courses yet? Coursera offers courses from well-known universities cheaply (or free, if you qualify). I think taking one of these will help you understand this more. Sometimes, the only way to understand some concepts is to take a course!
  6. Oct 14, 2016 #5
    Thanks @Fervent Freyja, I did take part of an epigenetics course on coursera about a year ago.
    I do understand the general picture of genetics. and how it works, it is a very large field, so easy to miss details. This question is rather specific, and I had a hard time finding an easily available answer online on it.

    What I am wondering is, out of all the DNA, that for example a muscle cell holds, the cell would expresses a certain number of "X" genes from their DNA that would create proteins that create the functionalities for a muscle cell. These "X" expressed genes are ONLY expressed for the muscle cell. Then, for example, for bone tissue would have Y genes that are ONLY for bone tissue genes. I was wondering wether muscle and bone tissues BOTH have some "Z" expressed genes in them? Plus, are there certain "A" genes that are in fact, expressed in all the cells in the whole body?

    I am guessing the answer is yes, and that it is a spectrum of certain genes that are expressed in all cells and then gradually other genes are expressed in certain organs, then groups of tissues that are similar, and then eventually get differentiated to very specific genes that are only expressed in specific tissues, or cells? This is of course, just my guess, I also imagine that it is very likely that there is no gene that is expressed in every cell of the body and that every cell has only specific groups of genes that drive its functionalities.

    I hope this clarifies where I am going with this question.

    P.S. also, as an additional example, I am wondering about fungi. I've heard before that fungi can stretch for miles, and that they are in a way a multicellular organism, but consisting of "individual fungus cells/organisms"? And I am guessing they would all be communicating through some gene that is expressed in all of them?
    Last edited: Oct 14, 2016
  7. Oct 14, 2016 #6
    What is a most fundamental property of living cells? Would not genes associated with such a property be expressed in every cell? First thing comes to my mind is mitochondria. Second is ribosomes. What about a protein that is used in transcription or translation? For that matter isn't a ribosome a large protein anyway? Do all cells have ribosomes?
  8. Oct 14, 2016 #7

    jim mcnamara

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    @aheight - good answer.

    Basic metabolic processes in Eukaryotic organisms, us for example, are at least 'booted up' by the common DNA, even if the cell no longer has DNA. So the expression of lots of genes exists anywhere a cell is still using glucose for energy, i.e., alive. Even if the DNA that created the enzymes and proteins for the process is currently not there.

    Examples:anaerobic respiration (Krebs cycle)/aerobic respiration -> cytochrome C oxidase.


    Think of it as a compiled executable, compiled somewhere, then written to an EPROM or similar device, then run in a device controller with no possible access to source code.... red blood cells.
  9. Oct 14, 2016 #8


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    As many have mentioned, there are a number of cellular structures and functions present in each cell (e.g. basic metabolism, the cytoskeleton, ribosomes, etc), and the genes associated with these structures and functions are present in almost every type of cell in a multicellular organisms. Such genes are called housekeeping genes
  10. Oct 14, 2016 #9
    This is just great! Thanks everyone for your responses.

    Basically, all species on Earth are therefore defined by all and any genes that are expressed in all the cells, in a bottom-up sequence, starting from the 355 genes that every cell on earth expresses, inherited from the Last Universal Common Ancestor, and then branching in all sorts of directions from there?
    from https://en.wikipedia.org/wiki/Last_universal_common_ancestor

    This begs another question in my mind, and that is, how does one define an "organism", since it is such a gradual process of organization and gene expression? After all, cells inside a multi-cellular organism are constantly replicating through mitosis, just like any other bacteria would. Wouldn't we say that all these cells are their own "independent organisms" that just happen to be also coded by some extra genes of the larger organism that they belong to? Plus, all the surrounding friendly bacteria that help the organism to survive, and all the other animals that the organism itself eats in order to survive, don't they create an event "bigger" organism, where they are all coded by their own set of genes and keeping the overall system "alive"?

    Sometimes it seems our world is an organism, inside of an organism, inside of an organism...
  11. Oct 15, 2016 #10


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    You might want to take a look at ecology and ecosystems.
  12. Oct 15, 2016 #11

    jim mcnamara

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  13. Oct 16, 2016 #12


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    In biology, species boundaries are defined by the ability to interbreed. Adding or removing genes, even if these genes control important phenotypes of the organism does not necessarily create a new species. A good example are dogs which, though selective breeding, exhibit a wide variety of phenotypes, yet still remain part of the same species.

    Also note that species is an artificial construct biologists have created in order to better categorize the natural world. The boundaries between species is necessarily fuzzy given that the concept of a species predates our understanding of evolution.

    Generally, the cells that compose a multicellular organism act in concert and are highly coordinated with each other. When this coordination fails and cells begin replicating independently of the rest of the organism is when diseases such as cancer arise. Interestingly, carcinogenesis has led to the creation of a new "species": an infectious face cancer among Tazmanian devils. Essentially, cancer cells in these animals evolved the ability to evade the immune system, allowing them to invade other animals and act as a parasite.
  14. Oct 16, 2016 #13
    This is all really fascinating. So basically, reproduction cells can keep mutating to create different "versions" of the same species, but there is a specific point where some gene or genes mutate in such a way, that the reproduction cells from that gene pool won't be able to reproduce with the rest of the organisms' reproduction cells?

    And I suppose this kind of mutation can happen to a single organism? Would it be a stretch to hypothesize that out of the billions of humans of the planet, there might be some humans somewhere right now that might have had a mutation in their reproduction cells that essentially makes them a "different species". To take this to an extreme, would it be plausible to suggest that the inability of some couples to have children might be due to the fact that they are "different species" and they don't even know it? ;)
  15. Oct 16, 2016 #14


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    Speciation occurs over geological timescale, so it takes many, many generations for species to diverge. Furthermore, speciation is not a black and white event, and there will necessarily be many intermediates between two distinct species.

    Speciation generally requires two populations of the same species to become reproductively isolated (e.g. split between two distant islands/continents), and during the time of reproductive isolation, the two species accumulate enough genetic differences to preclude interbreeding. Here's a nice blog post explaining how this could come about (though changes to the number of chromosomes in a species):

    See also this related PF thread: https://www.physicsforums.com/threa...olve-to-have-more-or-less-chromosomes.872635/
  16. Oct 19, 2016 #15
    Hi @Ygggdrasil quick question, I just got confused about to concept of species when it comes to bacteria, because they don't interbreed. I guess their "species" is then defined by the DNA they carry and the way that DNA differs from other bacteria around them. But then, we kind of lose the "dog breed" or in this case, a "bacteria breed" vs "bacteria species" distinction? What is the approach when it comes to bacteria and species clarification as opposed to animals that interbreed?
  17. Oct 19, 2016 #16


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    That's a great question, and one that biologists are currently grappling with.

    According to Wikipedia:

    The article describes some metrics that scientists apply (for example, the amount of DNA similarity between bacteria, along the lines of your thinking). In general, tracking evolutionary relationships among bacteria is a difficult problem because of the extensive horizontal gene transfer among bacteria.
  18. Oct 19, 2016 #17
    I also found this interesting article/interview on this topic.
    "...Bacteria do not have species. The rules for species naming do not apply to bacteria. But they need to have identity labels because of the practical importance in agriculture and health."
    "...You’d call them bacterial strains, or something like that. They definitely have some kind of identity. The genus name is more important than the species name. "
  19. Oct 19, 2016 #18


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    Although the biological species concept works well in many cases, there are exceptions where it does not seem to apply.

    There is often gene transfer between closely related species. Some well documented examples in the evolutionary past are the freshwater swordtails and platies (genus Xiphorphorus) and fish in the genus Danio (which contains zebrafish). Closer to home, Neanderthal vs. Homo sapiens vs. Denisovans have been shown to interbreed. So barrier between species? not always. Introgression is a term for genes going from one population or species to another through occasional hybridization followed by back crossing to one of the original populations.

    On the other hand, some sunflower species hybridize a frequently in the wild. When they do, they can make fertile hybrids which have four chromosomal sets (4n) instead of just two sets (2n, the normal diploid condition). These hybrid offspring can breed with each other but are reproductively isolated from their parents. Were they to breed with one of the parental species they would produce triploids (germ cells have 1/2 the n of the parents, 1n + 2n yields a 3n progeny). Triploids (in fish anyway) are generally viable, but not fertile. The unequal number of chromosomal sets do not divide up well in meiosis (to form germ cells).
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