The Talk.Origins Archive: Exploring the Creation/Evolution Controversy

The Period Gene of Drosophila
From the thread "A proposed table of contents for the book"

Post of the Month: April 2001
by Ian Musgrave

Subject:    Re: A proposed table of contents for the book
Date:       April 19, 2001
Author:     Ian Musgrave
Message ID:

G'Day All
Address altered to avoid spam, delete RemoveInsert

On 18 Apr 2001 10:39:46 -0400, "Adam Marczyk" wrote:

>Ian Musgrave & Peta O'Donohue wrote in message
I shouldn't be doing this, I'm up to my eyeballs in other work (curse
you Wilkins).
>> Hmm, has anyone thought of contrasting Paley's watch with the
>> Drosophila _Period_ gene, illustrating the difference between
>> designed and evolved watches?
>I haven't. What does that gene do?

Why, it's a watch. Or strictly speaking, it's the entrainment mechanism of a watch. The "watch" is the circadian rhythm generator in Drosophila, it consists of _Period_ _Timeless_ _Clock_ _Cycle_ and _Cryptochrome_, similar systems occur in mammals.

CLK and CYC form a dimer which binds to DNA and starts the transcription of PER and TIM, which then form a dimer and bind to other genes (clock controlled genes, CCG), causing their transcription. After a certain concentration of PER/TIM is reached, it inhibits its own transcription, the levels of PER/TIM fall and the CCG transcription is turned off. When PER/TIM falls low enough, transcription is de-repressed, and the cycle starts all over again. The system is a cyclic oscillator which acts as a "watch".

CRY is the light sensor, it entrains the PER/TIM cycle to the day/night cycle.

Unlike Paley's watch, where we know
a) That watches are manufactured
b) That watches (or their components) can't reproduce
c) That small changes in any one component are unlikely to produce an improvement in the watch

The Drosophila "Watch" can be fairly easily shown to have evolved. PER, TIM, CYC, and CLK show significant homology to the receptors that dimerise and translocate to the nuceus. These "watch" components are also quite similar to the simpler (blue light sensitive) watch (WC-1 and WC-2) that is present in the fungus _Neurospora_crassa_, and they are also related to the bacterial photoreactive yellow protein (sensitive to blue light). Overall, the "watch" looks like it arose fairly simply from proteins originally dedicated to blue light photoreception and transduction.

You can also show mutation within the watch components, eg mutations in PER can affect its function, a couple of amino acids difference between the PER gene in D. melanogaster and D. simulans, completely changes the timing of the song cycle. Mutations in other parts of the gene change the thermostability of the cycle, and clines of these mutations can be found with increasing latitude.

Overall, while Paley's watch implies design, the Drosophila "watch" implies evolution.

>> > b. No information-increasing mutations
>> Dembski vs Spetner vs Gitt
>> Misuse of Shannon and Kolmogorov/Chaitin information
>> "Function" vs "information"
>> Generation of novel functions, role of duplication
>> Nylonase as information increase
>> Evolved beta galactosidase operon as information increase
>> The Pentachlorliated aromatic degradation pathway (3 part
>> system, possibly IC) as information increase
>I also suggest we use the vancomycin resistance gene you pointed out some
>time ago as an excellent example of an information-increasing mutation. Ken
>Cox also provided an excellent proof of how natural selection increases
>information, namely that if you insist that _every_ genetic change is a loss
>of information, then for a mutation A->B and another B->A (such as reversion
>mutations), A would have to contain less information than A, which is

The vancomycin resistance gene is good, as it is a single point mutation that changes function, but the PAC pathway is better, as it is a _system_. Aw heck, we can put that one in too.

Cheers! Ian

Ian Musgrave Peta O'Donohue,Jack Francis and Michael James Musgrave
Southern Sky Watch

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