Text 1204, 101 rader
Skriven 2004-12-29 06:21:00 av Wirt Atmar (1:278/230)
Ärende: Re: Exactly what are "rec
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Malcolm writes, following Mike's assertion:

>> If someone wishes to clear understanding of recessiveness and dominance in
>> genetics then they will need to know a little bit more than simply the
>> meaning of 'gene'.
>>
>Our understanding of genetics is constantly developing. And "gene" is an
>important word that is in common use by non-scientists.
>
>There is no way of stopping someone from using the term "the gene for red
>hair", and by itself this does not necessarily indicate a misunderstanding.

Although the use of the term "the gene for red hair" may not be misunderstood
by the person using the phrase, it certainly promotes a misunderstanding in the
general population.

Almost invariably, when anyone speaks of a "gene for [fill in the blank]", the
"gene" is a defect (a defective variant of the instructions to properly build
some necessary component protein). The fundamental philosophical problem
underlying this misunderstanding is an attempt to too quickly assign causality
to a specific bit of code, particularly so in a system dominated by pleiotropy
(massive code re-use) and polygeny (many thousands of "genes" employed in the
construction of a single phenotypic feature), even if its use is just as
shorthand among professionals.

This assignment of casual credit or blame is a problem in all complex systems.
There is no way in the world to assign fitness values to the code that
specifies how a screw or a bolt is built and then say that *this* the code that
causes the airplane to fly. The function of flight is the result of the sum of
almost all of the individual blueprints that go into the construction of the
aircraft.

However the antithesis is possible. You can, with some accuracy, say that
*this* is the defective variant of the coding instructions (an "allele") that
causes a bolt to be mismanufactured and which subsequently results in the wing
falling off. The human tendency is then to call this a "gene for wing falling
off," but it's not true and it's a fundamental error to do so.

In complex systems, defects have very simple chains of causality, a simplicity
missing in the highly evolved, fully working system. When we don't know what
we're doing -- and we wouldn't call it "research" if we did -- we use these
simple chains of causality associated with defects as our means of exploring
the whole of the functioning system, but you can't take these explorations too
seriously. 

Professional biologists are often no better at this misuse than "civilians."
Medical geneticists have a pronounced tendency to speak of "oncogenes." When
the term first came into favor, the tendency was to say that these were
"cancer-causing genes." In recent years, I've noticed a more correct
redefinition of oncogenes, saying now that the gene, if mutated, has the
possibility of promoting neoplasia. Nevertheless, it remains a substantially
misleading term.

Mathematical genetics is perhaps even worse, institutionalizing the role of
defects and their simple causalities into its structure. If I had my way, I
would throw out almost all of the mathematics taught in genetics classes and
begin again, with a mathematics that more properly represents the informational
physics we now know to exist.

The fundamental problem is that if the nature of the "gene" is misrepresented,
a misrepresentation of the whole of the evolutionary process is unavoidable.
And such misinterpretations occur even among people who should know better.
Richard Dawkins wrote the following in his 1976 book, "The Selfish Gene:"

"Honey bees suffer from an infectious disease called foul brood. This attacks
the grubs in their cells. Of the domestic breeds used by beekeepers, some are
more at risk from foul brood than others, and it turns, out the difference
between strains is, at least in some cases, a behavioural one. There are
so-called hygenic strains which quickly stamp out epidemics by locating
infected grubs, pulling them from their cells and throwing them out of the
hive. The susceptible strains are susceptible because they do not practise this
hygenic infanticide... Rothenbuhler surmised that there might be two separate
genes, one gene for 'uncapping,' and one gene for ''throwing out'... This story
illustrates a number of important points... It shows that it can be perfectly
proper to speak of 'a gene for behaviour so-and-so'" (p. 64-66). 

Dawkins conclusion clearly misinterprets the nature of gene, after which he
goes on to derive a very strange philosophy around this misinterpretation,
"selfish genetics." As in all complex machineries, an infinity of failures may
bring the machine to a halt. The point failure of any single cog, sprocket, or
spring may be sufficient to cause the catastrophic failure of the entire
machine. But the inverse is clearly not true. No single sprocket, cog or spring
can generate complex behaviors as an isolated component. The more proper
question based on Dawkin's paragraph is: "It's clear that there exists at least
one single point failure that kills the hygenic infanticide response in
honeybees, but how many different genes, if defective, would do the same
thing?" The correct answer is probably hundreds.

This misrepresentation of genetic cause and effect permeates the professional
discussion, so if lay people are confused, we only have ourselves to blame.

Wirt Atmar
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