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What the heck is a gene anyway?
Feb. 22nd, 2007 01:17 amJohn Wilkins (at Evolving Thoughts) has a list of basic science concepts he thinks everyone should know.
The concept of "the gene" has attracted a fair bit of discussion, (I've only just noticed it but I haven't done a decent sciencey post for a while.)
Lots of different ideas.
Larry Moran doesn't like Dawkins' definition. His own is "a DNA sequence that is transcribed to produce a functional product". He doesn't include control regions, or other untranslated bits, but does include the translated bits that aren't used to make the protein/RNA (not all DNA makes proteins folks).
PZ Myers uses Griffiths, Lewontin Miller & Gelbart's book "Modern Genetic Analysis: Integrating Genes and Genomes" definition. "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."
Dr S.P. doesn't like this. She has "a problem with the words "chromosomal," "DNA," and I guess even, the phrase "the correct time and place during development." " Why? Well, cancer is triggered by genes being transcribed in the wrong time and place. Some genes are on nucleic acids that aren't DNA, and others on things that aren't chromosomes (and in HIV's case both). Her definition? "A gene is a heritable string of nucleotides that can be transcribed, creating a molecule with biological activity."
Dawkins (for those who haven't read the Selfish Gene [do so. now!]) says "A gene is defined as any portion of chromosomal material that potentially lasts for enough generations to serve as a unit of natural selection". While this means that Dawkins doesn't have to worry about the details of the gene its a rubbish definition if you actually want to look at the DNA/RNA you've got. Where does the gene start? Where does it end? Its at this point that you start refining it down and pinpoint specific locations, but for behavioural ecologists its often impossible to say how much of a behaiour is environmental, genetic or what combination of the two.
I think it all depends on who you're talking to. That and the fact that the word was invented in 1909 before we knew what DNA did.
For palaeontologists and evolutionary biologists a gene is a chunk of genetic information with a phenotypic effect. The internal structure of Hox genes isn't particularly interesting to me, what is interesting is how many of them there are, where they are expressed and how they are shared across phyla. I would lump the regulatory region in with the rest of the gene as a mutation here affects the gene's expression (and I wouldn't describe the regulatory region as a gene in its own right).
A behavioural ecologist could make do with something approaching Dawkin's definition of a gene. By the time a gene's effcts have made it to the outside world it doesn't matter if the change that distinguishes it and an allele is in the intron (the transcribed region), the cistron (the coding region), the regulatory regions, or another untranscribed portion.
To someone looking more closely this glosses over a whole world of complexity, sections of DNA coding for more than one product, non-transcribed bits affecting transcribed bits, products made form apparantley unrelated sections of DNA.
For my part, (in his comment on Pharyngula) Peter Ellis's definiton of: "A gene is a unit of DNA which is transcribed, has a phenotypic effect when transcribed, and whose phenotypic effect is altered by mutation" is, I think, the best one for the interested (or disinterested) layperson to start with. It doesn't worry about the fact that an awful lot of DNA gets transcribed at various points and doesn't do much that and If they then start to ask questions about how exactly these "gene" things work the detail comes in.
I know this means the control regions get excluded, but if its clear that thereare more things involved in a "gene" than just the gene itself then I don't think that matters. Maybe we need another word to argue about?
The concept of "the gene" has attracted a fair bit of discussion, (I've only just noticed it but I haven't done a decent sciencey post for a while.)
Lots of different ideas.
Larry Moran doesn't like Dawkins' definition. His own is "a DNA sequence that is transcribed to produce a functional product". He doesn't include control regions, or other untranslated bits, but does include the translated bits that aren't used to make the protein/RNA (not all DNA makes proteins folks).
PZ Myers uses Griffiths, Lewontin Miller & Gelbart's book "Modern Genetic Analysis: Integrating Genes and Genomes" definition. "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."
Dr S.P. doesn't like this. She has "a problem with the words "chromosomal," "DNA," and I guess even, the phrase "the correct time and place during development." " Why? Well, cancer is triggered by genes being transcribed in the wrong time and place. Some genes are on nucleic acids that aren't DNA, and others on things that aren't chromosomes (and in HIV's case both). Her definition? "A gene is a heritable string of nucleotides that can be transcribed, creating a molecule with biological activity."
Dawkins (for those who haven't read the Selfish Gene [do so. now!]) says "A gene is defined as any portion of chromosomal material that potentially lasts for enough generations to serve as a unit of natural selection". While this means that Dawkins doesn't have to worry about the details of the gene its a rubbish definition if you actually want to look at the DNA/RNA you've got. Where does the gene start? Where does it end? Its at this point that you start refining it down and pinpoint specific locations, but for behavioural ecologists its often impossible to say how much of a behaiour is environmental, genetic or what combination of the two.
I think it all depends on who you're talking to. That and the fact that the word was invented in 1909 before we knew what DNA did.
For palaeontologists and evolutionary biologists a gene is a chunk of genetic information with a phenotypic effect. The internal structure of Hox genes isn't particularly interesting to me, what is interesting is how many of them there are, where they are expressed and how they are shared across phyla. I would lump the regulatory region in with the rest of the gene as a mutation here affects the gene's expression (and I wouldn't describe the regulatory region as a gene in its own right).
A behavioural ecologist could make do with something approaching Dawkin's definition of a gene. By the time a gene's effcts have made it to the outside world it doesn't matter if the change that distinguishes it and an allele is in the intron (the transcribed region), the cistron (the coding region), the regulatory regions, or another untranscribed portion.
To someone looking more closely this glosses over a whole world of complexity, sections of DNA coding for more than one product, non-transcribed bits affecting transcribed bits, products made form apparantley unrelated sections of DNA.
For my part, (in his comment on Pharyngula) Peter Ellis's definiton of: "A gene is a unit of DNA which is transcribed, has a phenotypic effect when transcribed, and whose phenotypic effect is altered by mutation" is, I think, the best one for the interested (or disinterested) layperson to start with. It doesn't worry about the fact that an awful lot of DNA gets transcribed at various points and doesn't do much that and If they then start to ask questions about how exactly these "gene" things work the detail comes in.
I know this means the control regions get excluded, but if its clear that thereare more things involved in a "gene" than just the gene itself then I don't think that matters. Maybe we need another word to argue about?
