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

The "mechanism" as I have always heard it is, essentially, the concept of "it will become too degraded to function."There are bunch of lemmas that circle this concept. For example, the "no new information" concept. A mouse and an elephant have different numbers of chromosomes and, according to them, there is no way to add a new chromosome.This is generally buttressed by an inability to let 1 + 1 = 2. That is, assuming they don't outright deny the ability to have a new gene show up, they refuse to allow the addition of a gene followed by the alteration of that copy.If we assume that the genes are laid out abcdefg, then to have aabcdefg isn't "new information" because all we have done is copy what already existing, it isn't "new." But if we then alter than copy so that we have zabcdefg, that isn't "new" either because the length of the genetic string is identical to what we had before.In short, they have no memory. They only seem to remember what happened one step previous, not what we started with five or six steps ago. Yes, zabcdefg is the same length as aabcdefg, but we didn't originally start with aabcdefg. We started with abcdefg. And from that starting point, using methods that they accept as allowable, we have come up with something that has an additional, unique gene. Therefore, by any reasonable definition of "new," we have "added new information."But to counter this, they bring up the old saw of "no beneficial mutations." Ignoring the fact that most mutations are actually neutral, they latch onto the fact that most mutations that have obvious, visual effect are deleterious. Thus, they claim that if there is all this mutation going on inside, eventually these bad mutations will accumulate and cause unviability of the organism.This ignores selection. Yes, there are bad mutations, but those mutations are selected against. They happen, but they do not accumulate. Instead, the neutral and beneficial mutations collect, the ones that allow the organism to survive and thrive. And over time, we find that the species has changed with new information.Thus, their conclusion is that an organism can change, a little, but any large-scale changes cause inviability in the organism.

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Rrhain
WWJD? JWRTFM!

RAZD writes:

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can one develop a chromosome family tree?

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To some degree, at least, yes.If you look at the human chromosome 2, it looks exactly like a fused chromosome 2p and 2q of chimps, gorillas, and orangutans.Chromosomes have telomeres on the end...long strings of code on the end that essentially let the enzymes know that the end of the chromosome is coming up. If you look at the human chromosome 2, there is a telomeric sequence right in the middle of one of the branches. If you look at the tagging sequence, the rest of the chromosome below the telomeric sequence is a reversed version of the other primates chromosomes:Human:centromere-abcdefg-telomeric-zyxwvut-telomereChimp:centromere-abcdefg-telomere
centromere-tuvwxyz-telomereAnd while we're on it, there's the evidence of the centromere scar on the human chromosome 2. The full description:Human:telomere-123456-centromere-abcdefg-telomeric-zyxwvut-centromeric-0987-telomereChimp:telomere-123456-centromere-abcdefg-telomere
telomere-7890-centromere-tuvwxyz-telomereIt is quite clear that the human chromosome 2 is a fusion of ancestral chromosomes 2p and 2q: Human Chromosome 2 is a fusion of two ancestral chromosomes

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Rrhain
WWJD? JWRTFM!

RAZD responds to me:

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sweet. I knew there was a different number 42 (2x21) human and 46? (2x23) chimp?

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Just because I'm being pedantic:You do know those numbers can't be right. If I fuse two chromosomes into one, I have only lost one chromosome, not two. Thus, if humans are n (diploid), then chimps must be n+2 (diploid) and not n+4.OK...enough being pissy.Humans have 46, our close primate relatives have 48.

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also different number between horse and donkey is given as reason for the sterility of the mule.

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Yes, but that in and of itself is not sufficient. Przewalski's horse has 66 chromosomes compared to the common horse's 64. And yet, they can breed and produce fertile offspring...with 65 chromosomes.So yes, differing chromosomal count is a problem for producing fertile offspring, but it is not a "never" criterion.

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Rrhain
WWJD? JWRTFM!

pink sasquatch writes:

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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.

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Um, no.XO individuals develop as female. It's called "Turner's Syndrome." It is considered to be the most common chromosomal abnormality in humans (though only about 1% of those who have it survive to term).

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Rrhain
WWJD? JWRTFM!

RAZD responds to me:

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isn't Przewalski's horse smaller and genetically older?

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That I don't know. I'd have to look it up.

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Rrhain
WWJD? JWRTFM!

RAZD writes:

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

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Well, the effect of not having a sex-determining gene is different across species. In humans, for example, XO individuals are sterile and have other developmental abnormalities (not to mention that most XO fetuses fail to make it to term). In mice, however, XO individuals tend to be fertile. In horses, XO individuals are viable and have few physical differences, but tend to be irregular in their estrus cycles.YO individuals, however, are unviable in humans.In some species such as some insects, sex is not determined by the presence or absence of a sex chromosome per se. Instead, it is the ratio of sex chromosomes to autosomes. There is only one sex chromosome and if you have a greater ploidy of sex chromosomes to autosomes, you're one sex. Otherwise, you're the other.And then there's birds where the sex chromosomes go the other way: XX individuals are male and XY individuals are female.

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Rrhain
WWJD? JWRTFM!

RAZD writes:

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This is why you cannot breed horses to run at the speed of sound. There is a point where bones get too weak, heart and lungs not capable to keep pace even though the legs are "willing"

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The best example of this are the "double muscled" Belgian Blue cows. They have a genetic mutation in the myostatin gene, disabling it, which results in excessive hypertrophy of skeletal muscle cells. The bulls are so large that they tend to be incapable of breeding naturally: They would break the backs of the cows. Instead, they have to be ejaculated and the cows bred artificially or the bull needs to be put in a harness and lowered onto the cow.There is medical research done into how this can be used for human diseases such as muscular dystrophy...and worry that it would then be used as genetic doping by athletes.

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Rrhain
WWJD? JWRTFM!

pink sasquatch responds to me:

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And then there's birds where the sex chromosomes go the other way: XX individuals are male and XY individuals are female.

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

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True. As my bio text puts it, birds, moths, and butterflies have this trait of the males being XX and the females being XY and "to avoid confusion, this is usually expressed as ZZ (male) and ZW (female)."And with regard to XO, I understand now what you were talking about with the genes from the Y moving to other chromosomes.Sex determination is a varied and complex thing. Bees have diploid individuals being female and haploid individuals being male. Drosophila, however, it's the ratio of X chromosomes to autosomes. That is, XXN individuals are female (that is, XXO and XXY are female) while XN individuals are male (that is, XO and XY are male). Interestingly, XO males are sterile while XXY females are fertile. And then there's grasshoppers where females are XX and males are XO.

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Rrhain
WWJD? JWRTFM!

RAZD responds to me:

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and if you have XXY, XXO, XY and XO types which two get the free pass on the ark (assuming flies are not "clean" ... )?

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Well, the XO males are sterile, so they don't get to come. And if we're going to maintain the current genetic outcome, we'd need the XXY female so that the double-X gametes can be created.

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Rrhain
WWJD? JWRTFM!

pink sasquatch responds to me:

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Rrhain - I think it was you that mentioned "lesbian" lizards in one of the many homosexuality threads - all female but reproducing sexually.

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No, 'twasn't me. Alas, I don't recall who and I don't have the motivation to go looking.

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Are they really more like hermaphrodites?

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No, they are all female. This form of reproduction is called "parthenogenesis." In the particular lizards being discussed, they cannot reproduce unless they engage in sexual activity...but this activity doesn't actually result in any genetic material being exchanged. And since all the individuals are female, they're lesbian. The sex act triggers the reproductive cycle.There is another kind of lizard that switches between sexual and parthenogenetic reproduction, depending upon the conditions the population finds itself in. When variation is needed, males start being born to allow recombination and then they go back to all female.

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Rrhain
WWJD? JWRTFM!

Arachnophilia writes:

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i knew i was missing something. i suppose random mutation and genetic drift through transcription errors are still in play. i should stop posting on no sleep, i must sound like an idiot lol.

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No, I'm not so sure about that. One of the things that helps to keep bacteria going is their profligacy. They reproduce so quickly that even horrendous selection pressures can be stood up to because so many progeny are created.I don't think these lizards reproduce every 20 minutes.It would be interesting to see if there were any sexual reproduction in their history and if, given the appropriate pressures, they could flip to sexual reproduction as some other lizards do when variation is needed and then return to parthenogenesis when times are flush. It may be that we just haven't found the trigger.

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Rrhain
WWJD? JWRTFM!