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

Hey RAZD,A good question; my first thought: a possible mechanism would utilize a "kind"-specific subset of absolutely mutation-proof genes, perhaps involved in reproduction. These genes would represent the signature for each "kind" and thus define each kind.Potentially a designer could have designed most sequences to be mutable to allow micro-evolution, but the "kind" signature genes to be forever protected, preventing macro-evolution. Perhaps these genes would be "mutation-proof" because any single base change in their sequence would make the organism sterile or dead.Of course, there are no "mutation-proof" genes that I know of, so this is all for shits and giggles...

Would you restate this... particularly "gene development the same way it looks at mutations"?I'm not sure what you are getting at, since much work has gone into "how new genes evolve".

Yes. In fact, there is a group working on characterizing the "ancestral placental mammalian karyotype" - putatively the genome (at chromosomal segment level) of the mammalian species from which evolved all other mammals.A review on the project (a few years old): Original research from the same group (more recent): No, at a simple level, since separation/duplication/modification/addition/deletion of chromosomes is really separation/duplication/modification/addition/deletion of genes - the gene or regulation level changes effect evolution, whether micro- or macro-. Chromosome level changes do not, except when those changes result in alterations at the gene level.My personal bias is that structure of gene families and complexity of regulation will define macroevolution more than chromosome-level changes.

I'm in, perhaps as a "reasonable professorial type" - we might need a few of those to lend legitimacy.Perhaps after a year or two, when we've filled our coffers beyond our wildest dreams, we can slowly start slipping pro-evolution/anti-creationist propaganda in to really confuse the rubes...

Hey Nosy, What an idea you've tripped upon! If there is only a single "kind" that includes all life, then there is no need for this silly micro- and macro-evolution stuff, since evolution only occurs within "kind."But seriously, I think you're talking about certain basic gene domains that are translated into the individual activities of a protein - in many cases these are highly conserved (though I'm not sure if any are completely conserved, especially since neutral mutations would be allowed).These domains are important because they've allowed the evolution of countless genes with the same basic activity, but different overall activity due to differences in surrounding sequence or addition of other types of domains. Thus every single gene did not have to arise by chance, though the ancestral domain may have.In any case, these domains are short stretches of sequence - even highly conserved genes like those coding for the ribosomes are quite divergent in sequence, even if their activity domains are identical.I'd been interested to find out which gene holds the title for the most conserved sequence during evolution.

Depending on how a chromosome splits, or two chromosome fuse, there isn't necessarily a major detriment to the function of any of the genes on those chromosomes. The real problem is during cell division - depending on where the centromeres end up, huge chunks of genetic info can be lost or gained during division. In some rare cases in mice fusions have spontaneously arisen that don't wreak havoc on chromosome sorting and reproduction - if you are interested you might do a search on "Robertsonian translocations," since I'm feeling a bit rusty on the subject. (A similar example in humans is the Philadelphia translocation, though it hybridizes two genes, resulting in childhood leukemia...)I would think that if you had a small subpopulation arise with a chromosome fusion or division that was reproductively incompatible with the parental karyotype, you could potentially end up with reproductive isolation and speciation.As far as how splits/fusions/rearrangments occur, I'm fuzzy on the details, though I know they are a very active area of study. I know there are "recombination hot-spots" on some chromosomes that facilitate recombination errors (they are often large areas of repetitive sequence that confuse the DNA handling proteins). Chromosome breakage can occur with certain environmental insults (caffeine, for one, which is bad for coffee addicts like myself...), though they may have to occur after a fusion event so that following the break both pieces have a centromere to avoid loss during division.

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.

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

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...)

Potentially, but I think the issue is more a matter of 'natural variation' versus 'mutation.' One issue with the homeostasis experiments described above is the fact that they used artificial selection (instead of natural selection). Artificial selection essentially 'evolves' one or a few traits using existing natural variation (for the most part), and at the expense of all other traits - often it doesn't matter since the animals are captivity, free of all natural selection forces in the wild (imagine a pack of (artifically selected) dachsunds trying to compete with a pack of (naturally selected) wolves in the wild...)I guess I'm saying that these artificial breeding experiments don't tell us much about natural selection - where it is important to retain a certain degree of genetic 'flexibility'/adaptability while specialization evolves.But yes, you are correct in that anyone using the 'genetic homeostasis' experiments as refutation of macroevolution is simply ignoring the potential for mutation. I'm guessing if you repeated the Drosphilia bristle experiment with a population of flies given a chemical mutagen, the range of the phenotype would be extended.

Possibly, but it seems loss of enormous jaw muscles was a important milestone in allowing the capacity of the human skull to increase. For a very interesting paper:
http://www.ncbi.nlm.nih.gov/...
{Shortened display form of URL, to restore page width to normal - Adminnemooseus}Bigger also doesn't necessarily mean better; I'd like to think that further evolution of the brain will involve better utilization, rather than big bulbous heads...It is an interesting point though, a sort of chicken-or-the-egg kind of question. Which came first? Increased pelvic girdle or increased fetus size? (Hopefully the pelvic girdle for both parties involved, but I'm guessing it happened both ways through evolutionary history...)This message has been edited by Adminnemooseus, 07-07-2004 10:42 AM

hey RAZD, another interesting article regarding brain size evolution just appeared in PNAS - apparently binocular vision refinement is associated with increased brain size in primates:
From The Cover: Binocularity and brain evolution in primates - PubMed

You are referring to an entirely different context with Turner's Syndrome, that is, the sudden loss of the Y chromosome from the human genome as it currently stands.We were discussing it in an evolutionary context, and theories that the Y chromosome is gradually shrinking, and that necessary Y genes are jumping to autosomes and gaining new regulatory mechanisms.If the proponents of this theory are correct, in a 100,000 or so human generations there may be "XO" males.

It's my understanding that nomenclature is different when the female is heterogametic: "ZZ" males and "WZ" females.

Sure is... and you didn't even get into the hermaphrodites...Rrhain - I think it was you that mentioned "lesbian" lizards in one of the many homosexuality threads - all female but reproducing sexually.Are they really more like hermaphrodites?
Is it known if they have the equivalent of sex chromosomes?
Would "unisexual" be an apt term for their reproduction?If there's a decent publication out there I'd like to check it out.
(If I only imagined you talking about lesbian lizards, ignore me.)