Pharyngula

Basics: What is a gene?

I mulled over some of the suggestions in my request for basic topics to cover, and I realized that there is no such thing as a simple concept in biology. Some of the ideas required a lot of background in molecular biology, others demand understanding of the philosophy of science, and what I am interested in is teetering way out at the edge of what we know, where definitions often start to break down. Sorry, I have to give up.

Seriously, though, I think that what does exist are simple treatments of complex subjects, so that is what I’m aiming for here: I talk a lot about genes, so let’s just step way back and give a useful definition of a gene. I admit right up front, though, that there are two limitations: I’m going to give a very simplified explanation that fits with a molecular genetics focus (pure geneticists define genes very differently), and I’m going to talk only about eukaryotic/metazoan genes. I tell you right now that if I asked a half dozen different biologists to help me out with this, they’d rip into it and add a thousand qualifiers, and it would never get done. So let’s plunge in and see what a simple version of a gene is.

First, let me cite a single source that I used to pull this out: Modern Genetic Analysis: Integrating Genes and Genomes(amzn/b&n/abe/pwll) by Anthony J.F. Griffiths, Richard C. Lewontin, Jeffrey H. Miller, and William M. Gelbart. It’s an excellent genetics textbook, well worth the $116 if you’ve got the loose change jangling about. Here’s their definition of a gene:

A gene is an operational region of the chromosomal DNA, part of which can be transcribed into a functional RNA at the correct time and place during development. Thus, the gene is composed of the transcribed region and adjacent regulatory regions.

So we have long strings of DNA organized into chromosomes in each of our cells, and certain portions of that DNA will be copied or transcribed into RNA strands by various proteins in the nucleus. Which parts will be transcribed will depend in part on what proteins are present in a particular cell; the proteins have to bind to specific regions in the DNA to initiate the protein machinery to do the work of copying, and that machinery also recognizes certain regions of the DNA as places to stop copying. We have approximately 25,000 genes; the emphasis is on the “approximately” because one of the ways we identify genes is by looking for the punctuation marks of the start and stop regions, and there’s a lot of random punctuation scattered throughout the genome. The hypothetical designer must be a very poor copy editor.

Here’s a simple picture of a eukaryotic gene.

i-0e88f76d4f8289dac638f1bb409c3d01-simple_gene.gif

It has a few general parts. It’s on a strand of DNA, which you’ll have to imaging going off the screen to the left and right for a few miles in either direction. There is a regulatory region for transcription initiation (more about that in a little bit) which, if we include various enhancers and repressors, may stretch for many thousands of base pairs, with important short areas for regulation scattered throughout; one serious flaw with this diagram is that the regulatory regions comprise roughly twice as much DNA as the coding regions.

The part of the gene that is actually transcribed is broken up into regions called introns and exons. Introns aren’t going to be part of the final gene product, usually; enzymes are going to cut them out of the RNA and splice together those dark green exons to make the final functional RNA.

Let’s look at a specific example of a gene. The Online Mendelian Inheritance in Man database makes it easy to look up human genes with known functional roles, and I arbitrarily picked CFTR, the cystic fibrosis transmembrane conductance regulator. Follow that link, and you’ll learn far more than you ever wanted to about this gene that transports ions across cell membranes, and which is responsible for cystic fibrosis when it fails to work. It’s not basic, I’m afraid.

One of the things you can do from that gene entry, though, is take a look at a graphic portrayal of the gene on the chromosome. CFTR is one gene among many on the long arm of chromosome 7. You can also find the nucleotide sequence for the coding region here. Isn’t this informative?

    1 aattggaagc aaatgacatc acagcaggtc agagaaaaag ggttgagcgg caggcaccca
   61 gagtagtagg tctttggcat taggagcttg agcccagacg gccctagcag ggaccccagc
  121 gcccgagaga ccatgcagag gtcgcctctg gaaaaggcca gcgttgtctc caaacttttt
  181 ttcagctgga ccagaccaat tttgaggaaa ggatacagac agcgcctgga attgtcagac
  241 atataccaaa tcccttctgt tgattctgct gacaatctat ctgaaaaatt ggaaagagaa
  301 tgggatagag agctggcttc aaagaaaaat cctaaactca ttaatgccct tcggcgatgt
  361 tttttctgga gatttatgtt ctatggaatc tttttatatt taggggaagt caccaaagca
  421 gtacagcctc tcttactggg aagaatcata gcttcctatg acccggataa caaggaggaa
  481 cgctctatcg cgatttatct aggcataggc ttatgccttc tctttattgt gaggacactg
  541 ctcctacacc cagccatttt tggccttcat cacattggaa tgcagatgag aatagctatg
  601 tttagtttga tttataagaa gactttaaag ctgtcaagcc gtgttctaga taaaataagt
  661 attggacaac ttgttagtct cctttccaac aacctgaaca aatttgatga aggacttgca
  721 ttggcacatt tcgtgtggat cgctcctttg caagtggcac tcctcatggg gctaatctgg
  781 gagttgttac aggcgtctgc cttctgtgga cttggtttcc tgatagtcct tgcccttttt
  841 caggctgggc tagggagaat gatgatgaag tacagagatc agagagctgg gaagatcagt
  901 gaaagacttg tgattacctc agaaatgatt gaaaatatcc aatctgttaa ggcatactgc
  961 tgggaagaag caatggaaaa aatgattgaa aacttaagac aaacagaact gaaactgact
 1021 cggaaggcag cctatgtgag atacttcaat agctcagcct tcttcttctc agggttcttt
 1081 gtggtgtttt tatctgtgct tccctatgca ctaatcaaag gaatcatcct ccggaaaata
 1141 ttcaccacca tctcattctg cattgttctg cgcatggcgg tcactcggca atttccctgg
 1201 gctgtacaaa catggtatga ctctcttgga gcaataaaca aaatacagga tttcttacaa
 1261 aagcaagaat ataagacatt ggaatataac ttaacgacta cagaagtagt gatggagaat
 1321 gtaacagcct tctgggagga gggatttggg gaattatttg agaaagcaaa acaaaacaat
 1381 aacaatagaa aaacttctaa tggtgatgac agcctcttct tcagtaattt ctcacttctt
 1441 ggtactcctg tcctgaaaga tattaatttc aagatagaaa gaggacagtt gttggcggtt
 1501 gctggatcca ctggagcagg caagacttca cttctaatgg tgattatggg agaactggag
 1561 ccttcagagg gtaaaattaa gcacagtgga agaatttcat tctgttctca gttttcctgg
 1621 attatgcctg gcaccattaa agaaaatatc atctttggtg tttcctatga tgaatataga
 1681 tacagaagcg tcatcaaagc atgccaacta gaagaggaca tctccaagtt tgcagagaaa
 1741 gacaatatag ttcttggaga aggtggaatc acactgagtg gaggtcaacg agcaagaatt
 1801 tctttagcaa gagcagtata caaagatgct gatttgtatt tattagactc tccttttgga
 1861 tacctagatg ttttaacaga aaaagaaata tttgaaagct gtgtctgtaa actgatggct
 1921 aacaaaacta ggattttggt cacttctaaa atggaacatt taaagaaagc tgacaaaata
 1981 ttaattttgc atgaaggtag cagctatttt tatgggacat tttcagaact ccaaaatcta
 2041 cagccagact ttagctcaaa actcatggga tgtgattctt tcgaccaatt tagtgcagaa
 2101 agaagaaatt caatcctaac tgagacctta caccgtttct cattagaagg agatgctcct
 2161 gtctcctgga cagaaacaaa aaaacaatct tttaaacaga ctggagagtt tggggaaaaa
 2221 aggaagaatt ctattctcaa tccaatcaac tctatacgaa aattttccat tgtgcaaaag
 2281 actcccttac aaatgaatgg catcgaagag gattctgatg agcctttaga gagaaggctg
 2341 tccttagtac cagattctga gcagggagag gcgatactgc ctcgcatcag cgtgatcagc
 2401 actggcccca cgcttcaggc acgaaggagg cagtctgtcc tgaacctgat gacacactca
 2461 gttaaccaag gtcagaacat tcaccgaaag acaacagcat ccacacgaaa agtgtcactg
 2521 gcccctcagg caaacttgac tgaactggat atatattcaa gaaggttatc tcaagaaact
 2581 ggcttggaaa taagtgaaga aattaacgaa gaagacttaa aggagtgctt ttttgatgat
 2641 atggagagca taccagcagt gactacatgg aacacatacc ttcgatatat tactgtccac
 2701 aagagcttaa tttttgtgct aatttggtgc ttagtaattt ttctggcaga ggtggctgct
 2761 tctttggttg tgctgtggct ccttggaaac actcctcttc aagacaaagg gaatagtact
 2821 catagtagaa ataacagcta tgcagtgatt atcaccagca ccagttcgta ttatgtgttt
 2881 tacatttacg tgggagtagc cgacactttg cttgctatgg gattcttcag aggtctacca
 2941 ctggtgcata ctctaatcac agtgtcgaaa attttacacc acaaaatgtt acattctgtt
 3001 cttcaagcac ctatgtcaac cctcaacacg ttgaaagcag gtgggattct taatagattc
 3061 tccaaagata tagcaatttt ggatgacctt ctgcctctta ccatatttga cttcatccag
 3121 ttgttattaa ttgtgattgg agctatagca gttgtcgcag ttttacaacc ctacatcttt
 3181 gttgcaacag tgccagtgat agtggctttt attatgttga gagcatattt cctccaaacc
 3241 tcacagcaac tcaaacaact ggaatctgaa ggcaggagtc caattttcac tcatcttgtt
 3301 acaagcttaa aaggactatg gacacttcgt gccttcggac ggcagcctta ctttgaaact
 3361 ctgttccaca aagctctgaa tttacatact gccaactggt tcttgtacct gtcaacactg
 3421 cgctggttcc aaatgagaat agaaatgatt tttgtcatct tcttcattgc tgttaccttc
 3481 atttccattt taacaacagg agaaggagaa ggaagagttg gtattatcct gactttagcc
 3541 atgaatatca tgagtacatt gcagtgggct gtaaactcca gcatagatgt ggatagcttg
 3601 atgcgatctg tgagccgagt ctttaagttc attgacatgc caacagaagg taaacctacc
 3661 aagtcaacca aaccatacaa gaatggccaa ctctcgaaag ttatgattat tgagaattca
 3721 cacgtgaaga aagatgacat ctggccctca gggggccaaa tgactgtcaa agatctcaca
 3781 gcaaaataca cagaaggtgg aaatgccata ttagagaaca tttccttctc aataagtcct
 3841 ggccagaggg tgggcctctt gggaagaact ggatcaggga agagtacttt gttatcagct
 3901 tttttgagac tactgaacac tgaaggagaa atccagatcg atggtgtgtc ttgggattca
 3961 ataactttgc aacagtggag gaaagccttt ggagtgatac cacagaaagt atttattttt
 4021 tctggaacat ttagaaaaaa cttggatccc tatgaacagt ggagtgatca agaaatatgg
 4081 aaagttgcag atgaggttgg gctcagatct gtgatagaac agtttcctgg gaagcttgac
 4141 tttgtccttg tggatggggg ctgtgtccta agccatggcc acaagcagtt gatgtgcttg
 4201 gctagatctg ttctcagtaa ggcgaagatc ttgctgcttg atgaacccag tgctcatttg
 4261 gatccagtaa cataccaaat aattagaaga actctaaaac aagcatttgc tgattgcaca
 4321 gtaattctct gtgaacacag gatagaagca atgctggaat gccaacaatt tttggtcata
 4381 gaagagaaca aagtgcggca gtacgattcc atccagaaac tgctgaacga gaggagcctc
 4441 ttccggcaag ccatcagccc ctccgacagg gtgaagctct ttccccaccg gaactcaagc
 4501 aagtgcaagt ctaagcccca gattgctgct ctgaaagagg agacagaaga agaggtgcaa
 4561 gatacaaggc tttagagagc agcataaatg ttgacatggg acatttgctc atggaattgg
 4621 agctcgtggg acagtcacct catggaattg gagctcgtgg aacagttacc tctgcctcag
 4681 aaaacaagga tgaattaagt ttttttttaa aaaagaaaca tttggtaagg ggaattgagg
 4741 acactgatat gggtcttgat aaatggcttc ctggcaatag tcaaattgtg tgaaaggtac
 4801 ttcaaatcct tgaagattta ccacttgtgt tttgcaagcc agattttcct gaaaaccctt
 4861 gccatgtgct agtaattgga aaggcagctc taaatgtcaa tcagcctagt tgatcagctt
 4921 attgtctagt gaaactcgtt aatttgtagt gttggagaag aactgaaatc atacttctta
 4981 gggttatgat taagtaatga taactggaaa cttcagcggt ttatataagc ttgtattcct
 5041 ttttctctcc tctccccatg atgtttagaa acacaactat attgtttgct aagcattcca
 5101 actatctcat ttccaagcaa gtattagaat accacaggaa ccacaagact gcacatcaaa
 5161 atatgcccca ttcaacatct agtgagcagt caggaaagag aacttccaga tcctggaaat
 5221 cagggttagt attgtccagg tctaccaaaa atctcaatat ttcagataat cacaatacat
 5281 cccttacctg ggaaagggct gttataatct ttcacagggg acaggatggt tcccttgatg
 5341 aagaagttga tatgcctttt cccaactcca gaaagtgaca agctcacaga cctttgaact
 5401 agagtttagc tggaaaagta tgttagtgca aattgtcaca ggacagccct tctttccaca
 5461 gaagctccag gtagagggtg tgtaagtaga taggccatgg gcactgtggg tagacacaca
 5521 tgaagtccaa gcatttagat gtataggttg atggtggtat gttttcaggc tagatgtatg
 5581 tacttcatgc tgtctacact aagagagaat gagagacaca ctgaagaagc accaatcatg
 5641 aattagtttt atatgcttct gttttataat tttgtgaagc aaaatttttt ctctaggaaa
 5701 tatttatttt aataatgttt caaacatata taacaatgct gtattttaaa agaatgatta
 5761 tgaattacat ttgtataaaa taatttttat atttgaaata ttgacttttt atggcactag
 5821 tatttctatg aaatattatg ttaaaactgg gacaggggag aacctagggt gatattaacc
 5881 aggggccatg aatcaccttt tggtctggag ggaagccttg gggctgatgc agttgttgcc
 5941 cacagctgta tgattcccag ccagcacagc ctcttagatg cagttctgaa gaagatggta
 6001 ccaccagtct gactgtttcc atcaagggta cactgccttc tcaactccaa actgactctt
 6061 aagaagactg cattatattt attactgtaa gaaaatatca cttgtcaata aaatccatac
 6121 atttgtgtga aa                                                    

That sequence will be translated into a protein in the cytoplasm of the cell, which will then go on to be incorporated into the membrane, where it will work to regulate the secretion of chloride and other ions. I confess, I’m often not so much interested in what the coding region of the gene does as I am in how the gene is turned on or off in the first place, so let’s look at how that’s done.

Here’s another cartoon of a gene. The green part is the piece of DNA that is to be copied into an RNA transcript, and the piece of protein machinery that is going to do that job is called RNA polymerase, the pink rectangle. RNA polymerase is going to advance sequentially along the DNA, matching each DNA nucleotide on one strand with a complementary RNA nucleotide, and catalyzing the linkage of each RNA nucleotide to its neighbor. RNA polymerase needs to know where to start, though — it doesn’t just land on a random part of the genome and start copying away — and it looks for a region called a promoter (in red).

i-d00f0968458b7d4f61c9cbb7f846604c-simple_gene_reg.jpg

Part of the promoter is a relatively simple sequence called the TATA box, because it contains lots of A and T nucleotides. The TATA box is bound by a whole constellation of transcription initiation proteins, though, building up a complex that promotes the binding and activity of RNA polymerase. The DNA itself has a 3-dimensional structure that folds around and allows sequences called enhancers and silencers to play a role in controlling transcription by way of intermediary proteins called activators and repressors. Turning on a gene is a family affair, requiring the participation of many proteins.

i-c2b79baa3f6a30cc90e90cf6ee0ceb2e-simple_control.jpg
The molecular apparatus controlling transcription in human cells consists of four kinds of components. (The numbered proteins are the names of subunits of RNA Polymerase II. Each subunit is named according to its molecular mass in kilodaltons.) Basal transcription factors (labeled A, B, F, E H) are essential for transcription but cannot by themselves increase or decrease its rate. That task falls to regulatory molecules known as activators and repressors. Activators, and possibly repressors, communicate with the basal factors through coactivators—proteins that are linked in a tight complex to the TATA-binding proteins, the first of the basal transcription factors to land on the core promoter.

The really complicated part of the diagram above, of course, is that each of those colored blobs is a protein, which is in turn the product of expression of a gene elsewhere in the genome, which has in turn its own promoter and enhancers and silencers. The coding region in this cartoon could, for instance, be for one of the components of that RNA polymerase complex in action here. Genes can make gene products that affect the expression of other genes by binding to the regulatory regions or to the proteins that are involved in the regulatory complex.


One last thing: I also took a look at the other common web source for definitions of basic concepts, Wikipedia. Here’s the first line of the Wikipedia entry for “gene”:

A gene is the unit of heredity, with each gene determining one inherited feature of an organism.

That is completely wrong. “One gene, one character” is a false idea of the relationship of genes to inheritance, since many genes contribute to the appearance of a single feature, and one gene will play a role in many different features. Apparently, the next basic ideas I should summarize are polygeny and pleiotropy.

Comments

  1. #1 Griststone
    January 16, 2007

    “A gene is the unit of heredity, with each gene determining one
    inherited feature of an organism.”


    That is completely wrong. “One gene, one character” is a false idea of the relationship of genes to inheritance, since many genes contribute to the appearance of a single feature, and one gene will play a role in many different features.


    But this *is* the functional definition of the gene as portrayed by Dawkins in the Selfish Gene. He essentially argues that biologists derive genes backwards from different phenotypes, and, elsewhere, that a gene is best understood as the potential difference between two otherwise identical organisms:

    When a geneticist talks about a single gene effect, he is always talking about a difference between individuals. A gene ‘for brown eyes’ is not a gene that, alone and unaided, manufactures brown pigment. It is a gene that, when compared with its alleles, in a normal environment, is responsible for the difference in eye colour between individuals possessing the gene and individuals not possessing the gene. The statement ‘G1 is a gene for phenotypic characteristic P1′ is always a shorthand. It always implies the existence, or potential existence, of at least one alternative gene 2, and at least one alternative characteristic P2. It also implies a normal developmental environment, including the presence of the other genes which are common in the gene pool as a whole, and therefore likely to be in the same body. If all individuals had two copies of the gene ‘for’ brown eyes and if no other eye colour ever occurred, the ‘gene for brown eyes’ would strictly be a meaningless concept.

    The metaphor matters. It must map to the more scientific defintion; otherwise, popular science books like Selfish Gene are inherently deceptive. I have to assume that Dawkins “believes” in “one gene, one character,” even if he “knows” better.

  2. #2 Steve LaBonne
    January 16, 2007

    Griststone- this is why I don’t even like the word “gene” and wish we could somehow get rid of it (I know, fat chance). Dawkins is simply talking like a classical geneticist in that passage, and as PZ warns in his post the referent of “gene” in that world maps very imperfectly indeed onto what molecular biologists think of as a gene.

  3. #3 David Marjanovi?
    January 16, 2007

    There probably are such books, but I don’t know any…

    and I have read books about what happens inside a cell – nuclear physics (??)

    No, cell biology/molecular biology/…

    BTW, keep in mind that proteins and DNA strands are humongous molecules made from the combination of smaller molecules (with water as a byproduct in both cases).

  4. #4 David Marjanovi?
    January 16, 2007

    There probably are such books, but I don’t know any…

    and I have read books about what happens inside a cell – nuclear physics (??)

    No, cell biology/molecular biology/…

    BTW, keep in mind that proteins and DNA strands are humongous molecules made from the combination of smaller molecules (with water as a byproduct in both cases).

  5. #5 David Marjanovi?
    January 16, 2007

    “Powers of Ten” is good, but quite brief.

  6. #6 David Marjanovi?
    January 16, 2007

    “Powers of Ten” is good, but quite brief.

  7. #7 thwaite
    January 17, 2007

    For a completely operational definition of ‘gene’ I’ve always been fond of George Williams’ (1966):

    ‘In evolutionary theory, a gene could be defined as any hereditary information for which there is a favorable or unfavorable selection bias equal to several or many times its rate of endogenous change.’

    … this is a conceptually challenging encapsulation even when one knows that the endogenous changes he’s referring to are those like crossover and mutation. But it’s a useful and generalized definition, and so was cited by Dawkins in his Extended Phenotype book, and at least implicit throughout the Selfish Gene – which nowhere details any specific gene. It didn’t have to – this conceptual gene suffices.

  8. #8 Griststone
    January 17, 2007

    Sparc,

    I probably wasn’t sufficiently clear in my previous post. I understand that biologists can use a definition of “gene” that works for thier specific experimental needs, and that this may differ from the definition used by a geneticist. But the fact that different disciplines use such divergent operational definitions begins to suggest that there really is no such “thing” as the gene. In other words, it’s a model we are straining to preserve in the language, based on old atomistic ideas about matter and biology.

    For the layman, genetics is increasingly more difficult to conceptualize, as it grows increasingly imporant as a matter of policy, e.g. stem cells research, gene therapy, genetic engineering, not to mention the gene-centric evolutionary views of Mr. Dawkins, which, intentionalyl or not, have an impact on the way we view humanity.

    One is tempted to draw the conclusion that the paradigmatic shift in genetics and molecular biology has already occured, but no one has taken the time to inform the lay community, perhaps because explaining it would be such a difficult task. I say this half tongue-in-cheek, but with the serious suggestion that the “gene” concept has done its share of heavy lifting and should presently yield to a new model.

  9. #9 Torbjörn Larsson
    January 17, 2007

    We may not be able to agree on a common gene definition.

    Inability to find an encompassing definition isn’t peculiar to biology but the existence here of at least 7 definitions of a gene (Ridley, apparently) and 26 definitions of a species (Wilkins) points to the real difficulties to get a feel for this elephant.

    But IMHO we should not expect that all phenomena are simple and amenable for a specific reduction. It isn’t exceptional if a more exact description will contain models based on a set of different definitions.

    As a layman, I would find it helpful if it is made clear which of these definitions is referred to in posts. Actually, I would expect it from a more serious treatment as well.

    The market of ideas should weed out bad or unnecessary definitions. Some other considerations could help. Moran pointed out when defining evolution that it is good to distinguish mechanisms from the definitions that describe them, making the later general and flexible terms.

    Btw, that reminded me of the distinction and separation of syntax and semantics in logics, math, computer science – perhaps also here the application (the semantics, what does the definition mean) could be kept out of it too to make it even more flexible. For example, why “biological evolution” instead of “evolution” when some of the same mechanisms can be used for software applications?

  10. #10 Torbjörn Larsson
    January 17, 2007

    “what does the definition mean” – what does the definition refer to

  11. #11 Peter Ellis
    January 18, 2007

    I don’t think “A unit of DNA that is transcribed” is a useful definition – for the simple reason that there’s too much of it! There are plenty of documented examples of intergenic transcription, and plenty of examples of transcribed pseudogenes.

    But by the same token, we can’t restrict it to protein coding genes. The majority of functional RNA in the cell is non-coding – even if you restrict yourself just to the ribosomal RNAs and tRNAs, let alone the various other types of ncRNA species.

    I think that we have to ultimately fall back on function – we could define a gene as a stretch of DNA that is transcribed and which has a phenotypic effect when transcribed.

    That would include protein coding genes and non-coding genes, but exclude transcribed pseudogenes. Unless we find that the transcribed pseudogene has an effect (e.g. on regulation of the cognate coding gene) – in which case I certatinly think we *should* upgrade its status from pseudogene to non-coding gene.

    One final qualification is necessary. Consider that intergenic transcription is thought to have effects on chromatin structure (one hypothesis is that a way of clearing out old histones and replacing them with new variants is to send down an RNA polymerase to “bulldoze” the old ones out the way). Under the above description, this would be included as a “gene” – a useless definition as some substantial fraction of the entire genome is translated at some point (albeit at extremely low levels).

    A way of distinguishing genic from intergenic transcription is that intergenic transcription is thought to lead to fairly general chromatin effects, not dependent on the DNA sequence. Any phenotypic effect thus wouldn’t be expected to change due to mutations in the intergenic region.

    So, a final description, and the best I can offer, is that “A gene is a unit of DNA which is transcribed, has a phenotypic effect when transcribed, and whose phenotypic effect is altered by mutation”

    Note that this takes us to something resembling the Dawkins definition – which you’re all misinterpreting hideously. He is *not* saying that “one gene, one function” is always true – it’s simply that at the start of the paragraph he explicitly says that he’s considering the case of single-gene effects, presumably for simplicity’s sake.

  12. #12 MartinC
    January 18, 2007

    Greg, I guess we may be talking cross purposes here. My own personal view as to what a term like ‘gene’ should encompass is much more similar to Dawkins ‘replicator’ definition than the central dogma style DNA that codes for an mRNA that produces a specific protein. Most functional RNAs are regulated at a transcriptional level in a manner not too different from protein encoding transcripts. Indeed many non-coding RNAs carry out functions analagous to proteins (forming scaffolding for ribonucleoprotein complexes, modifying target mRNAs etc). They are non protein encoding however they are genes.

  13. #13 Henry Gee
    March 31, 2008

    “I realized that there is no such thing as a simple concept in biology”

    Evolution by Natural Selection is as simple as simple can be. Heritable variation, oversupply of offspring, and lots of time. What could be simpler?

    Makes you wonder what the fuss is all about, really :)

  14. #14 leejoe
    June 30, 2008

    this is just one part of gne to made.there’re trillions trllions and trillions genes not find ways
    j

  15. #15 Candy DeBerry
    October 27, 2008

    The legend for the figure of the molecular apparatus controlling transcription in human cells is incorrect. It states “(The numbered proteins are the names of subunits of RNA Polymerase II. Each subunit is named according to its molecular mass in kilodaltons.)”

    The numbered proteins are NOT subunits are RNA Pol II. They are different TAFII proteins (TATA-binding protein Associated Factors for RNA Pol II). Together, the TATA binding protein (TBP) and the TAFIIs make up general transcription factor TFIID.

The site is currently under maintenance and will be back shortly. New comments have been disabled during this time, please check back soon.