Talk:Evolution/Inheritance and genetics

Moved from Talk:Evolution --Brion 23:17 Jan 19, 2003 (UTC)

Inheritance and genetics as they apply to evolution

In the text of the evolution article it states:

In Darwin's time, there was no widely accepted mechanism for heritability. In modern times, the mechanism for heritability is known to be DNA. There is also the interesting possibility that proteins are responsible for some heritability.

I have a couple problems with this. First, DNA is a structural molecule and does nothing on its own. Therefore, it is not a mechanism. The mechanism of heritability is the process known as reproduction. To use an analogy, people are confusing the act of reading for the book being read.

Second, I'm trying to imagine how a protein could be a means by which traits are inherited and its awfully hard to see. In animals at least those proteins would be restricted to being in cell lines that evolve into sperm and egg. If anyone has scientific evidence for such I'd love to see a link rather than see this comment ad hoc. -- dwm.

Proteins can affect inheritance in (at least) two ways:

1. They may be modified post translationally, and then cause other polypeptides of the same type to be modified in the same way. Prions and histones do this in a manner that propagates traits thru mitosis and mieosis.

2. Gene expression states can also be self-perpetuating. This self-perpetuation involves proteins (obviously).

I have no reason to believe that this affects in vertebrate inheritance, but there is evidence that it does affect yeast inheritance, and possibly plants also. I don't think that there's any reason to mention this type of inheritance in the Evolution article, but we shouldn't write anything that implies that these types of inheritance don't exist. AdamRetchless 23:19, 20 Mar 2004 (UTC)

Yes, you're confused, but I think the text is fine as it is. First, where do you get the idea that there's some black-and-white distinction between data-carrying elements and functional elements at the molecular level? Biochemistry isn't that simple. Certain strands of RNA, for example, can catalyze reactions by themselves, without being transcribed into proteins. I don't think anyone has shown DNA doing this, but I don't think it would terribly surprize anyone either. Secondly, I think the statement is being used in a more general sense than you're interpreting: DNA is a means by which heredity takes place. Maybe "mechanism" isn't the best word, and there are certainly lots of other pieces in the whole mechanism as well, but DNA does play a central role as the primary means of long-term storage of information. I think that's all they're trying to say here. The comment about proteins is potentially confusing, but it probably refers to recent discoveries about proteins that make their way into germ cells, mostly sperm. I'll try to find a citation. --LDC

Let me be plain. The reference chain for the protein heritability carries directly to prions, which are infectuous agents. I'm more likely to get a prion by eating my Mom as opposed to inheriting it. More so, they affect neural tissue, not germ cells. As well, even if they were capable of self-assembly in a soup of amino acids (which I *doubt*), they still are diseases and not something heritable. Finally, as all prion prteins are minor structural variants of normal proteins that are assembled from regular, central dogma controlled paths, there is no reason to believe that prions actually violate the central dogma in the first place.

As such, if I don't see a reference in a reasonable period of time, I think we'd be better off deleting that sentence as opposed to keeping it. Further, the whole concept of an inheritable protein suggests that the protein _encodes_ information that affects my cell lines in a non-germ way. Having 1 protein from my pop in a sea of billions isn't enough to claim heritability; I'll get more proteins (unwanted) from viral infections in my lifetime.

Finally, histone and histone-like binding proteins may be said to have an effec t on 'expression' of proteins, but a couple histones I get from my Dad aren't going to have much effect on a mature adult with billions of cells. Histones, can, in theory, affect 'expression', but they carry no information per se, nor can they reproduce independently. They're as dependent on the central dogma as any other protein. Which of course, begs the question: if I didn't inherit that information from my Dad, how can I make those proteins in sufficient quantity to even make a difference?

The more I think of it, the more difficult I see the task of justifying a protein based scheme of heritability. The protein has to hitch a ride in egg or sperm, else its not inherited. The protein must then appear in quantity in both germ and cell lines, and must do so without *any* central dogma support (i.e. the protein must be capable of self assembly), else the protein is a consequence of the central dogma itself, not in opposition to it. The protein in question must do something useful that helps the organism to survive, else its simply a parasite, not a property of the human condition. Those are very difficult and stringent conditions, and really shouldn't be idly tossed into the soup, if the goal of this pedia is accuracy.dave

I agree, it's a pretty speculative possibility only likely to influence to evolution of things like bacteria--certainly nothing as large as a human. So it probably doesn't need to be mentioned here. --LDC

Ok, I altered the sentence that bothered me most to:

In Darwin's time, there was no widely accepted in-depth mechanism for heritability. In modern times, the molecule that allows for heritability is known to be DNA, and the commonly accepted mechanism of expression of heritable information is called the Central Dogma

The reason being that the basics of reproduction had to be known in Darwin's time, that having sex led to offspring who had traits inherited from parents. Microscopes existed then, I'm sure von Leeuwenhook had seen sperm by then. What wasn't known was the mechanism of heritability at a molecular detail. I don't care for my writing and would invite others to think of a better way of expressing these notions. Dwmyers

When Darwin first published evolution, Jenkins came up with a very solid objection on the grounds that any individual variations would be watered down as they spread throughout the population, to the point where they effectively didn't exist. Mendelian genetics fixed that. I think the point here was to explain that.

Dear Graft,

You removed my reference to prions, saying that it wasn't relevent. While a discussion of the nature of inheritance is not absolutely necessary in a section about natural selection, if we are to discuss genes we should also discuss other means of heretible variation such as prions and epigenetics. Perhaps all of this should go into a different section addressing the nature of variation. (as should the comment about natural selection permitting the long term survival of life, since it is variation that permits the long term survival of life. Natural Selection = Death) adam

Hi Adam... I removed the reference to prions because I don't think it has much to do with heritable variation as it relates to evolution or natural selection, especially insofar as the forms of prions found so far seem to be diseases that kill within a generation. So, while they might be taken as a form of 'heritable variation' from a certain point of view, they don't represent a) a significantly sized class of heritable variation when compared to heritable variation due to genes, b) heritable variation if you take that to mean something transmitted consistently across many generations, and c) a mechanism for selective pressure (beyond the selective pressure induced by having some prionic disease, i.e., instantaneous death).

Genes should definitely get first priority, but heretible prions have been thoroughly examined (see True and Lindquist "A yeast prion provides a mechanism for genetic variation and phenotypic diversity" Nature, 407, pg 477 (28 september 2000). Here's a quote about Lindquist's work:

Both yeast and mammalian prions transmit phenotypes via protein-protein interactions, in which an abnormally shaped prion protein influences its normal counterpart to assume an abnormal shape. In mammalian prion infection, such abnormal, insoluble shapes cause protein clumping that kills brain cells. In yeast cells, however, the insoluble prion protein is not deadly, but it alters protein synthesis. http://www.hhmi.org/news/lindquist4.html

In this example, prions do have all of the traits that you listed above.

Epigenetic factors are I suppose interesting and worth discussing, but I think we'd be better off just saying that what we're talking about is DNA, not genes, since this would include chromosome rearrangements and such and would preclude a larger and unnecessary discussion of the types of DNA variations we're talking about within the body of this Evolution article. Graft

Genetic and epigenetic factors have different means of inheritance; epigenetic factors (and prions) have the ability to "convert" similar genetic factors, and this conversion ability can be influenced by environmental factors. Granted, we don't know of many examples where these were influential, so genes should get the main emphasis, but I believe that once we understand more about the mechanisms behind prions and epigenetics, we will find more examples of them.

Well, frankly I think epigenetics is a bit faddish, but I haven't read an extraordinary amount on it. At any rate I think at this point most of the interesting aspects of epigenetics rest on speculation and the people who write/study it are interested in building it up to be more than it probably is. Sure, it might have dramatic implications for evolution, but then, the far side of Alpha Centauri might be made of Swiss cheese, and think of the dramatic implications that has... Soy muy esceptico. Graft

Maybe this should be addressed in biological inheritance

Edited the heredity and genes section. There were some glaring errors eg. Genes were defined as chains of amino acids. Fixed this, significantly changed th heredity section and added the types of mutations ie. point and chromosomal. --MattDal 12:00, 17 Jul 2004 (UTC)

Evolution view point for dicussion

THE ETERNAL QUESTION??

The evolution of life forms has been a matter for discussion over the centuries. The discussion has been progressed by philosophers, scientists, astro physicists, religious doctorines, politicians, astronomers and astrologers and most other disciplines in society.

As such, one cannot discount or disregard any of these thought processes. Each discipline has its own benchmarks for validation and verification of their doctrines.

These disciplines, even though on the face of it, are mutually exclusive, but one has to accept the possibility of cross integration between them.

The possibility of a supreme being has been given the name of God or Allah or Bhagwan or Jehovah or supreme energy or a superior alien race or the great white light, amongst other nomenclatures.

One thing common amongst all these through civilisations, is the analogy to something which humans have considered a power superior to themselves. Religion has relied on blind faith. Scientists are in a quandary, as the basis of science is the ability to explain something implicitly. This is not possible, when it is knowledge beyond civilisations current understanding at that time.

There was a time when cultures believed in aspects of nature as the Supreme Being. Some still do. However, every time civilisation develops understanding of something, it leads to the question of what created that which is understood. And once again, the debate and discussion resumes where it started.

Scientists believe that they know everything, well almost. But if one considers any point in time in history, the human race thought what they knew then was the ultimate truth. Any other thoughts were suppressed in one for or another. However, it is in the human nature, of SOME (I will return to this later on), to push against the boundaries of current understanding and progress it in some way.

Where would we be without people like Krishna, Buddha, Moses, Mohammed, Jesus, Homer, Socrates, Aristotle, Egyptian pyramid architects, Leonardo D Vinci, Mendelssohn, Christopher Columbus, Darwin, Bach, Mozart, Albert Einstein to name just a few. Each was radical in their doctrines in their lifetime.

The argument I put to people who advocate that human understanding about everything has progressed so much, that there is very little yet to be discovered! If this was the case, would we not still believe that the world was flat? Would we know about the number ZERO? (If that can be classed as a number!!)Would we know how to pasteurise milk? Would we know about space and other galaxies and planets? Would we appreciate that light can bend round corners? Would we understand the speed of light and time? Would we understand that an atom could be split? Would we know that machines as small as a pin head could perform trillions of calculations per second? There are a whole plethora of instances, where knowledge has been undergone a quantum leap. So to discount the possibility of such an event happening again is surely not a defendable argument. It is a comfortable situation to let others do the thinking and exploring for some. Expediency is comforting but rarely moves knowledge further. There has to be a position, a very high one, for radical thought. We have to aim higher than our reach, WHAT ELSE IS A HEAVEN FOR??

Let us start from a view point of not trying to reinvent the wheel. If we assume the statement of various doctrines as true.

If we consider a pyramid structure of gene proliferation. ‘The Selfish Gene’(Dr.Richard Dawkins) principle, though a valid theory, I feel is not complete in itself.

Same is true for natural selection (Charles Darwin) as a representation of evolution.

If we consider, that the real meaning of life is self propagation of the gene pool. The genes are pre-programmed to behave in a certain manner. However, there are different types of genes. Starting from the MASTER genes at the top of the pyramid, with the common genes at the bottom. The shape of the multi dimensional pyramid holds a constant ratio of angles, much akin to the ratios of the ‘magic triangle’. The number of genes at the bottom is proportionately greater than those above it and so on until we reach the top. Natural selection occurs at each level. Thus, at the bottom, natural selection occurs at a larger number than above it, however, the net effect is less apparent.

This also explains why in earlier civilisations and cultures, communication between the bottom and top of the pyramid seems easier. This is because the distance between them is smaller. As civilisations have expanded, the greatest increase has been at the bottom on the pyramid, as a result, increasing the distance to the top.

At any point in time, genes are programmed more directly by the ones immediately above it and so there is a greater dilution from the top.

What about the other side of the coin? DEVIL? SHAITAN? SATAN?

Well this too forms a pyramidical structure.Only; it is a mirror image of the ‘GOOD’ pyramid.

The battlefront is at the interface of the two pyramids at each level. Depending on who wins, dictates which pyramid grows faster than the other.

This also leads to explain the concept of Armageddon, Judgement Day, Kalyug, End of the World scenarios, amongst other similar concepts.

It would be close minded to assume that the top and for that matter, the bottom of the pyramid exist on Earth. There is no reason why we are not just somewhere in the pyramid. The top and for that matter the bottom may be on another battlefront. Earth is simply one part of the whole picture.

However, some estimation can be made. If we look at the population at any given point in time on earth, (one that we can measure), we can interpolate backwards and forwards to gain an insight to a frame of reference and infer a possible scenario for the future.

This aspect of research and debate and discussion can benefit from using the power of the brain.Well, surely two minds is better than one, and so far onwards exponentially.

There are various other ideas to explore. I would very much appreciate input from others on this.

Monami, it seems you and I stepped on each other putting this back. Sorry about that. Please procede, as long as you don't remove the comment. Thanks. -Harmil 10:36, 15 August 2005 (UTC)[reply]