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 Newsgroups: talk.origins Date: April 19, 2001 Author: Ian Musgrave Message ID: qlfeOq6Nkm3SJcCVE7q1IYDITtga@4ax.com
On 18 Apr 2001 10:39:46 -0400, "Adam Marczyk"
>Ian Musgrave & Peta O'Donohue
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
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.
[snip]
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
[snip]
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?
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
>> > 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
>absurd.
=====================================================
Ian Musgrave Peta O'Donohue,Jack Francis and Michael James Musgrave
reynella@werple.mira.net.au http://werple.mira.net.au/~reynella/
Southern Sky Watch http://www.abc.net.au/science/space/default.htm