"Macro" vs "Micro" genetic "kind" mechanism?

As far as I understand it you both tripped over the DIFFERNCE of orthogonalities and paralleisms but as Lam's tone thinks he can fake this I will leave to search my own posts in the matter. Best Brad.

Actually that's a very controversial point - the Nature paper a year or so ago that was the most comprehensive examination of the Y chromosome thus far demonstrated that the Y has some tricks that give it stability - one is that it folds to "pair" with itself during time of meiotic recombination to give more stability (which has led to some masturbating Y-chromosome jokes since all other chromosomes pair with another chromosome...)Also, even if the Y chromosome did disappear in a few hundred thousand years, there would still be men, they'd just be XO instead of XY.

caffeine?NOOOOOooooooooo.

heh - same thought occured to me. wonder where that leaves the ark scenario though ...

what I get for going from memory isn't Przewalski's horse smaller and genetically older?

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

I believe there are some species where the sex determining gene is missing.

That's easy - a pair of LUCAs... and nothing else...

butwould they still be wrong?

I know. I was only joking.

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The Laminator

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and perhaps the flood is the universe, life landing on this poor forsaken rock and saying "hey, luca what we got here ..."

I figured so much - it was good for the discussion anyway. (I'm now considering making my next career move into studying sex determination for the next few years, so I've got XX, XY, XO, ZZ, ZW, on the brain...)

not XXX?

Might as well get a Ph.D. in oral sex.... Sorry, just saw one of those corny Woody Allen movie.

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The Laminator

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quote:

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Creationists do even better, Phillip Johnson in his collection of mistatements, out of context quotes, and outright lies otherwise known as the book Darwin on Trial, claims that species possess a genetic limit to variation. This is stated as a "fact" in his book yet no supporting evidence or reference to such a limit is given. This fictional limit is used to explain the barrier between micro and macro evolution.

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What Johnson and other anti-evolutionists are going on about, as best as I can determine, is the phenomenon known as 'genetic homeostasis'. What this means is that populations undergoing intense directional selection (as in agricultural breeding programs) will often stop responding to selection for the trait at a certain point, accompanied with reduced fitness.Anti-evolutionists often cite Drosophila work done by Mather and Harrison, where they selected for increased numbers of abdominal bristles, as an example of limits to natural selection (and by extension, macroevolution). At some point the number did not increase beyond 36, as I recall. Anti-evolutionists jump on this, crowing that there is a limit to variation beyond which natural selection cannot go.Well, in a certain, obvious sense, they are right, but the Mather and Harrison example is not an illustration of their thesis. I Michael Lerner, the geneticist who coined the term 'genetic homeostasis' noted that it was not that the reduced fitness was caused by the population running out of variation, but that the intense selection for one trait, common in breeding progranms, disrupted gene complexes that had co-evolved over a long period of time in nature, and the reduced fitness was the response to this disruption.KCThis message has been edited by KCdgw, 07-06-2004 10:10 AM

So the homeostasis would hold until a mutation in those co-evolved genes occurs to allow a new level to be reached?Could this be a mechanism for punctuated equilibrium?

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}