Talk:Polymorphism (biology)

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[edit] Structural polymorphism

Someone should do a section on structural polymorphisms.

If you mean anatomical/gross morphology polymorphisms, this is common in plants. Like light/shadow leaves (on the same plant). Ontogenetic variation in leaf shape might also be considered structural polymorphism, though ontogenetic variation is generally considered a separate thing - it cannot be induced, like seasonal polymorphisms, but follows a set course. Dysmorodrepanis 23:02, 16 August 2007 (UTC)

[edit] Hard to understand

And the examples suck. --218.215.133.116 11:20, 16 July 2006 (UTC)

Replace them with better ones. An explanation here of why those examples are better would be great. —JerryFriedman 18:32, 21 December 2006 (UTC)

What really sucks is the main definition. A polymorphism is a "discontinuous genetic variation that results in the occurrence of several different forms or types of individuals among the members of a single species". Correct me if I'm wrong, but polymorphism is just a sequence variation and doesn't necessarily cause different phenotypes217.209.218.154 16:31, 5 March 2007 (UTC) 217.209.218.154 16:30, 5 March 2007 (UTC)

Polymorphism in the general sense indicates merely the presence of multiple character states (of any character) in an interbreeding population. Limiting it to sequence variation is just one of those examples of gene-jockeys trying to usurp a general term for their (hence, only important) uses. This usurpation has caught on, to some extent, but I don't like it. Another thing worth mentioning here is that, last I checked, it wasn't entirely clear that melanism in peppered moths is genetic. Maybe I missed something. Paalexan 22:13, 27 March 2007 (UTC)
You don't happen to have a definition with a source, do you? Or an example of a non-genetic polymorphism? It would be something like the sex of alligators being determined by the temperature at which the eggs incubate, right? —JerryFriedman 04:35, 28 March 2007 (UTC)
Example of apparent non-genetic (= mutational, it is epigenetic/biochemical... obviously) polymorphism: Araschnia levana. Such cases are not actually rare; the alligator thing is one too. Dysmorodrepanis 22:54, 16 August 2007 (UTC)

[edit] Hair color

So blond hair, despite being rarer, isn't going to dissapear because blondes are more successful? --euyyn 19:56, 19 November 2006 (UTC)

I think blond hair is unlikely to disappear because it has little effect on reproductive success (except possibly in the tropics, since it's associated with light skin?). But I don't know any facts on this point. —JerryFriedman 18:32, 21 December 2006 (UTC) (My hair isn't blond, but it's disappearing.)
Well, you know, maybe it's just culture, but here in Spain we like blondes more, in general. Nothing to do with skin color, since we also like tanned women more... (Although I've heard that in Germany, where everybody is blond, we dark-haired people are considered more handsome).
In school they told me that the blond gene is recessive, and because of that it will likely dissapear in the future. I must confess I never understood that implication, since being recessive doesn't mean being less likely to pass to your offspring... But when I read this article I realized that, if they really are more succesful (stadistically), then blondes could not dissapear...
Heck, if should have studied Biology... --euyyn 15:00, 25 December 2006 (UTC)
I think you're right to question what they told you in school. I too see no reason that a recessive gene should disappear.
Also, maybe blondes in Spain get asked to dance first, but that doesn't mean they have more children. If you think about the people you know who have the most children, I'll bet you won't see much correlation with hair color. (In fact, I don't think the number of children correlates with attractiveness. "Siempre hay un roto para un descosido.") If I'm not mistaken, the birth rate in Germany, the Netherlands, Britain, and Scandinavia is low, for socioeconomic reasons. If that's true and it continues, blondness could get less common in the world. —JerryFriedman 05:13, 26 December 2006 (UTC)
My line of thought was more like "women/men who end up alone are likely the less atractive ones". Since the number of children of those who have isn't correlated with atractiveness, this would be important in the long term. Another question is wether the children of an atractive couple are o aren't atractive... But I agree that demographic distribution is a stronger factor. Anyway, what's the relation between this and polymorphism? Thanks for your enlightenment. --euyyn 19:43, 8 January 2007 (UTC)
Common sense says less attractive people should be more likely to end up alone, but that's not my observation. I have no data, though. And this has nothing to do with polymorphism, since that seems to be just discontinuous variation. Oh well. —JerryFriedman 04:50, 25 March 2007 (UTC)
Yeah, the "blonde" allele (alleles?) are not decidedly unfit about anywhere in the world, and that's the only thing needed to maintain them for the time being. The fate of the individual matters in population genetics as regards genetic drift etc, but not in general. Dysmorodrepanis 22:57, 16 August 2007 (UTC)

[edit] Merge

I think the concepts and examples fit together, and it would be nice to have one definition of "morph". —JerryFriedman 04:48, 25 March 2007 (UTC)

Polymorphism as from biology, which would include the geneticists definition, as that is the realm it falls under has nothing to do with "morph" phenotypes. Polymorphism is separately defined it is its own important word describing a certain GENETIC occurance at the allele level of the genome. My biology classes elaborate extensively on "polymorphism" with no mention of the term "morph." I feel that all this merging of articles will only lead to more confusion as they are separate terms so should have separate definitions and articles in wikipedia, otherwise why don't we just combine everything and scrap the whole project. —The preceding unsigned comment was added by 24.56.204.204 (talk) 00:20, 6 May 2007 (UTC).
Sorry to take so long to answer. I can assure you that some whole-organism biologists use "polymorphic" to refer to different "morphs" or phenotypes. If the geneticists' definition is different, maybe there need to be two articles on polymorphism, one for genetics and one for whole-organism biology including what's currently at morph.
You could ask your professors whether they consider the visible morphs mentioned in the article to be examples of polymorphism.
Anyway, the question is what topics belong together and what don't. If we can reach a consensus on that (and I hope that "we" gets bigger than just you and me), no doubt people will organize the articles appropriately. A satirical suggestion to "combine everything and scrap the whole project" doesn't convince anyone of anything or help reach any conclusion. —JerryFriedman 23:18, 13 May 2007 (UTC)
The reason why most textboods don't discuss morphs in their discussion of polymorphism is that the term has no formal standing in zoology, and botanical nomenclature tends to split non-specialists' heads right open. I can assure you (24.56.204.204) that the "morphs" of zoology are precisely what you describe: allelic polymorphisms (as a rule-of-thumb, about 80% of morphological polymorphism has an allelic basis, the rest is developmental or otherwise imprinted).
As regards the merge, support but article needs entirely reworking. Silent mutations and haplotypes might be mentioned (a genetic polymorphism with no/no obligate phenotypical equivalent). Also, if we're at it, merge form (zoology), form (botany), variety (botany) and subvariety here too, link to Botanical nomenclature and discuss the different "categories" of polymorphisms. (After all, while zoological morphs are allele variants, form- and variety-type polymorphisms may not be. Especially not in plants, where polyploidy and clonality causes things to work very, very much differently. Which is why the botanical terms have formal standing in nomenclature, whereas the zoolological ones have none.)
JF, if you execute the merge, I'd be happy to help build this section I mentioned. If that's OK and when you go ahead, drop me a line. I have always been dissatisfied with having to sift through all those stubs (you should have seen the morph article before I went over it, gack!) Dysmorodrepanis 16:31, 1 June 2007 (UTC)
Okay, I'll probably do the merge within a couple days. I think we can write the article with the overlapping but not identical definitions used in different specialties and thus address the issues raised by 24.56.204.204. I'll take a shot at organizing the article, but I can't do the details. I'll let you know.
Should we namecheck Mendel? But what I'm really hoping for in this article is a few examples that are not familiar from high-school and introductory college biology. —JerryFriedman 04:11, 2 June 2007 (UTC)
I'd be honored to dig up some examples. I have a lengthy paper here entitled "The evolution, maintenance and adaptive function of genetic colour polymorphism in birds" which I wanted to work into WP anyway :D As for other examples, I'll go get some butterflies, plants, spiders... Dysmorodrepanis 10:14, 2 June 2007 (UTC)

[edit] expert tag

This article really needs work by someone who can answer questions like those raised above, and no doubt other questions that haven't been brought up yet. For instance, we're not talking about sexual dimorphism, or queens and workers and soldiers, or anything related to age, right? What about haploid and diploid yeast? Aphids? Another plant example or two? Bacteria? So I tagged it. —JerryFriedman 04:43, 28 March 2007 (UTC)

I think I should be able to answer this, or most of it. Most of the things you mention here are not generally considered polymorphisms, but technically they are; a brief sentence pointing to the appropriate article (such as polyploidy) would do the job. Dysmorodrepanis 16:33, 1 June 2007 (UTC)

[edit] To do

In looking for really good definitions of polymorphism (does it include differences between allopatric populations?), I'm finding good examples: ecological polymorphism in white clover and a slightly frustrating look at non-genetic seed polymorphism in Dimorphotheca (which unfortunately doesn't seem to be named after this attribute). —JerryFriedman 02:05, 3 June 2007 (UTC)

A source for castes of social insects as polymorphisms. —JerryFriedman 03:59, 3 June 2007 (UTC)

[edit] What is and what isn't a polymorphism

The definitions I've found seem to think that a polymorphism has to occur in a single population. In that case Form (zoology) and Variety (botany) don't seem to qualify. I didn't mention haplotypes because it's too late at night for me to figure out what they are.

Maybe we need a "see also" kind of section on things that aren't polymorphisms. —JerryFriedman 04:15, 3 June 2007 (UTC)

[edit] Genetic polymorphism

I'm able to do a bit of writing now; I'll do it here and you can decide whether/how it fits with the article.

[edit] some definitions

these might be useful at least to see if we agree on basic terms to use in the article.

  • phenotype: the organism as produced by genetics and development; the aspects which interact with the environment. Includes visible parts and also behaviour, physiology &c. [this is not the definition given on WP, which is incorrect]. The phenotype living in its environment may or may not be successful in having descendents.
  • genotype: the genetic constitution of an individual; the set of genetic elements which partly produces the phenotype, and which may be passed on by inheritance.
  • gene: a segment of nucleic acid which contains the information to produce a functioning RNA product.
  • allele: one of the DNA coding groups (~variants of a gene) which occupies a given locus on the chromosome.
  • pleiotropism: pleiotropy is when a single gene influences multiple phenotypic traits. Consequently, an alernative allele may have an effect on all those traits simultaneously, but perhaps unequally.
  • polymorphism: means 'many forms'; includes a) visible and non-visible characters, b) which may be continuous or discrete and c) wholly, partly or not inherited. Despite their name, SNPs (single nucleotide polymorphisms) are a misnomer; they are not polymorphisms as the term is normally used.
  • genetic polymorphism: Genetic polymorphism is the occurrence together in the same locality of two or more discontinuous forms of a species in such proportions that the rarest of them cannot be maintained just by recurrent mutation (Ford 1940). Whew! Let's not hit the readers with that right away! The definition has three parts: a) sympatry; b) discrete forms, and c) not maintainable just by mutation. And I think the definition rules out heteropatry.

Now I can start on the real stuff... Macdonald-ross 16:26, 16 August 2007 (UTC)

Looks like a great start, but I have some questions and comments, possibly related to my weak knowledge of biology.
  • Why are SNPs not polymorphisms? They seem to fit the definition.
  • because they are part of the genotype. Taken for granted is a general conceptual separation which was first made clear by August Weismann, who used the terms soma and germ plasm, until the T.H. Morgan period whose terminology in genetics lasts into the present-day. Germ-plasm = complement of genes = genotype; Soma = what's produced using information provided by genes = phenotype. Francis Crick's Central Dogma of DNA is another way of putting it: Once information has passed into protein it cannot get out again. By 'information' is meant the exact sequence of bases and hence amino-acids. [see discussion, with refs, in Judson H.F. The eighth day of creation 1979 p336-8]. If we use polymorphism both for point mutations and for the phenotypes that might be affected, we will get into profound confusion.
  • We've got a source that says that polymorphisms have to be discrete, and as I recall, I found several more. If we're going to say they can be continuous, we need a source for that too.
  • distinction needs to be made (as it is in defs above) between general differences in phenotype (called polymorphism above) and genetic polymorphism (sometimes called balanced polymorphism), which is the subset which many ecological geneticists (eg Ford) think is the most interesting from an evolutionary point of view.
  • I'm not sure what you mean by saying Ford's definition rules out heteropatry (a word I just looked up). Do you mean that according to Ford, consistent differences between heteropatric populations must or can't be polymorphisms?
  • because in heteropatry (not a common term, I agree) the two (or more) groups are not interbreeding even though they're in the same area. In genetic (balanced) polymorphism the interbreeding population includes all the forms. So heteropatry is similar to allopatry in that it effects reproductive isolation which might (or might not) lead to speciation. Genetic (balanced) polymorphism does not do this.
  • Also, I think this answers your original question, which was: 'Why did you add a note that polymorphism was not geographic variation?'. It's because the morphs are all part of the same interbreeding population (of course, naturally, they do have to occupy space!). Generally speaking, the phrase geographical variation is taken to mean that the forms under study occupy different spaces, possibly overlapping to some extent.
I'm fine with making the definition easier to assimilate than Ford's. —JerryFriedman 01:46, 17 August 2007 (UTC)
  • Whew! I'm worn out! — but your questions are both intelligent and pertinent. By achieving clarity on these points and others we will be helping readers who may well have similar questions in mind. This is helpful. Regards, Macdonald-ross 15:13, 18 August 2007 (UTC)
It's a lot easier to ask questions than to answer them, so I appreciate the answers. It's also much easier to criticize than to write, so I want to avoid working by the method of you writing and me criticizing. (I've been subjected to that.)
The problem with restricting "polymorphism" to the phenotype is that the geneticists use it to mean differences in genotype. I think we really have to address that usage in this article—not only SNPs, but also RFLPs and whatever. Either that, or as suggested above, we need an article on phenotypic polymorphisms and one on genotypic. —JerryFriedman 23:32, 19 August 2007 (UTC)
SNPs and RFLPs are terms invented by the molecular biology teams doing base-sequence analysis. If they had been geneticists they would have called them SNAs (single nucleotide alleles)! Seriously, though, we must avoid molecular analysis of genetic material a) because there isn't room to do it properly; b) other pages are already doing it; c) it would seriously interfere with the ecology/genetics slant of the present article, and hence d) it would make the article too complex for most readers. We could use the device "see SNPs and RFLPs for other uses of the term polymorphism." Macdonald-ross 14:11, 20 August 2007 (UTC)

[edit] some examples

We meet genetic polymorphism every day of our lives since our species (like most other eukaryotes) uses sexual reproduction, and of course, the sexes are differentiated. The system is relatively stable (with about half of the population of each sex) and heritable by means of sex chromosomes. Every aspect of this everyday phenomenon bristles with questions for the theoretical biologist. Why is the ratio ~50/50? How could it arise from an original situation of asexual reproduction, which has the advantage that every member of a species could reproduce? Why the visible differences? These questions have engaged the attentions of biologists such as Ronald Fisher, John Maynard Smith and William Hamilton, with some success.

There are a large number of less spectacular examples of human genetic polymorphisms. All the common blood types, such as the ABO system, are genetic polymorphisms. Here we see a system where there are more than two morphs: the phenotypes are A, B, AB and O are present in all human populations, but vary in proportion in different parts of the world. They are seemingly never eliminated by natural selection; and why not? Statistical research has shown that the various phenotypes are more, or less, likely to suffer a variety of diseases, which suggests that the pleiotropic effects of the genes set up opposing selective forces, thus maintaining a balance.

The situation is best seen in sickle-cell anaemia, which is found mostly in tropical populations in Africa and India. An individual homozygous for the recessive sickle haemoglobin, Hgb S, has a short expectancy of life, whereas the life expectancy of the normal homozygote and the heterozygote is normal. So why does the sickle cell variant survive in the population? Because the heterozygote is resistant to malaria and the malarial parasite kills a huge number of people each year. This is a balanced genetic polymorphism, balanced between fierce selection against homozygous sickle-cell sufferers, and selection against the other homozygotes by malaria. The heterozygote has a permanent advantage (a higher fitness) so long as malaria exists; and it has existed as a human parasite for a long time.

(plan to move on to experimental systems in insects) Macdonald-ross 18:02, 16 August 2007 (UTC)

This is very interesting and I didn't give it enough emphasis in the present draft, but you seem to want to go straight to the stability of polymorphisms, and I'm wondering about the order. Maybe we should say first that polymorphisms are the raw material of selection. Then the question of why selection doesn't give us "monomorphy" gains more force. So maybe an order like this:
  • Definition
  • of polymorphism
  • A few examples to explain what we're talking about and show the variety of polymorphisms (visible and invisible; appearance, behavior, development, physiology; discrete and continuous; heritable and not).
  • Yes.
  • Selection (brief)
  • of what?
Of traits—natural and artificial selection. —JerryFriedman 23:32, 19 August 2007 (UTC)
  • How polymorphisms can be stable
  • This is where I plan to offer most, followed by a readable definition of genetic (balanced) polymorphism.
  • More examples of the endless variety of life, with short evolutionary explanations or statements that they're not theoretically understood.
  • no objections, though must write this last.
What do you think? —JerryFriedman 02:35, 17 August 2007 (UTC)
Also, there's already an article Evolution of sex, so maybe we should mention this special case briefly with a link to that article.
By the way, ABO comes from surface antigens of red blood cells, not hemoglobin. —JerryFriedman 04:42, 17 August 2007 (UTC)
  • Yes, re link to evolution of sex; yes re blood groups, corrected! Shouldn't write late at night... Macdonald-ross 15:37, 18 August 2007 (UTC)
Okay, sounds like we have a plan here (unless someone comes up with a better one). —JerryFriedman 23:32, 19 August 2007 (UTC)


[edit] related articles

I'm sure there's more. In particular, if balanced polymorphism really does its job, then we don't need to put so much detail into this page. Macdonald-ross 17:23, 20 August 2007 (UTC)

Balanced polymorphism looks pretty good to this amateur, although the mosquito example here is way less cliché than the Pepperered Moth at balanced polymorphism.
But you've got an excellent point: we really do need to look at what WP already has. —JerryFriedman 21:52, 20 August 2007 (UTC)

[edit] para 2 needs correcting

Para 2 reads: "Not all polymorphisms as defined above are genetic, but in genetics the term is reserved for variation in a population's DNA." I think this is both wrong and incomplete (if that's possible!). DNA is a red herring, see my final para under definitions above.

Firstly, I think the word polymorphism as used by biologists always describes an heritable condition, even if sometimes environmental effects also play a part, sometimes as a trigger. If you think I'm wrong, please give counter-examples. Since polymorphisms are heritable, they always involve selection, and genetic polymorphism results from a balance of selection on different morphs.

For Araschnia levana as a polymorphism without genetic variation, see The Principles of Insect Physiology, by Wigglesworth (1947). (Snippet views, but search for "polymorphism" and "Araschnia levana".) In the 1984 edition of Insect Physiology, Wigglesworth refers to castes in social insects and sexual/parthenogenetic variation in aphids as polymorphisms.
This is what's commonly called the Map Butterfly. The trigger is indeed environmental: if pupae are cooled in their first 24 hours the spring variety develops; if not, the summer variety forms. Of course, it does have a genetic basis, and is polymorphic but not genetic polymorphism. That's why I chose the term heritable. Macdonald-ross 15:42, 22 August 2007 (UTC)
Several of the papers in The Karoo: Ecological Patterns and Processes, edited by Dean and Milton (1999), refer to variation in seeds produced by ray flowers compared to disk flowers as polymorphism. (The variations can include germination rates and thus have similar flexibility advantages to some genetic polymorphisms.)
Sorry, don't know enough about this to comment!
Insect Hormones, by Nijhout, mostly uses "polyphenism", but the two occurrences of "polymorphism" seem to refer to non-inheritable features.
Now I find polyphenism is in WP! Will add to list above; thank you. The common theme seems to be discrete morphs triggered environmentally. The genetic basis has undergone selection; and therefore must be heritable. The system is polymorphic but not genetic polymorphism. Macdonald-ross 15:42, 22 August 2007 (UTC)
Ecology: Individuals, Populations, and Communities, by Begon, Townsend, and Harper (which might be a good reference), defines polymorphism as variation and then specifically defines genetic polymorphism.
The text on p40 actually uses the phrase selectively relevant variation (not simply 'variation') by which they mean variation with a genetic basis (otherwise it couldn't be selected). Variation is a much more general term; genetic variation and to a lesser extent genetic diversity come closer to what we're talking about, and I'll add the first to the list, too! Macdonald-ross 15:42, 22 August 2007 (UTC)
On the other hand, Selected topics in Medical Genetics, by Clarke, specifically excludes seasonal variation as in Araschnia levana from the definition of polymorphism.
The web extract suggests they are denying it the status of genetic polymorphism (to which I agree) and not discussing polymorphism generally. Macdonald-ross 15:42, 22 August 2007 (UTC)
I think this article is the place to be clear about the varying definitions in use. In fact, "polymorphic" is polymorphic—though I hope there are no sympatric variations, that is, contradictory definitions in the same book. —JerryFriedman 21:50, 20 August 2007 (UTC)

Secondly, a distinction is needed between:

For sure. By the way, Begon, Townsend, and Harper mentions an interesting type of transient but apparently balanced polymorphism: propagules from one region drifting into another. —JerryFriedman 21:55, 20 August 2007 (UTC)

Finally, I offer an expanded version of para 2 on the main page, which I'm hoping will stand up to your scrutiny! Macdonald-ross 16:40, 22 August 2007 (UTC)

[edit] Next steps

I propose expanding the examples section, and making clear what they are examples of; and making sure each of the distinctions above are illustrated by at least one example. Macdonald-ross 19:51, 22 August 2007 (UTC)

Sounds great. —JerryFriedman 22:01, 23 August 2007 (UTC)

[edit] My changes and other comments

I don't think "an heritable" is generally accepted. The NSOED mentions "an" before "h" only if the first syllable is unaccented.

"inheritable" maybe? Dysmorodrepanis 22:41, 23 August 2007 (UTC)
heritable is the basic term, and occurs in genetic literature as the general adjective. an before h is perfectly acceptable in GB; a before h also. Up to about 1950 the form 'an hotel' was almost universal in England; now one does see the alternative. Macdonald-ross 13:33, 24 August 2007 (UTC)
I'd love to discuss this at length, in Talk if you're interested. Thanks for making less of an issue of it than I did. —JerryFriedman 22:01, 27 August 2007 (UTC)

If we're really not going to cover genetic polymorphisms, I think we have to change the name of this article to something like "Polymorphism (phenotypic)" and have a disambiguation page. By the way, why are only "certain" variations in DNA considered polymorphisms?

Oh but we should. Discuss what allele variants are, differential expression etc. In most cases a summary of main articles. But since polymorphism is something fixed (at least in the life of the individuum) and (usually) inheritable, it's obvious that genetics must be given its due space, methinks. And then you have things like Single nucleotide polymorphisms in normal/sickle hemoglobin of course. I think I remember the rule -of-thmb that 70-80% of polymorphism has a genetic base and most of the rest is epigenetic but still inborn (= fixed and possibly even heritable), e.g. by temperature.
See for example Chromosomal polymorphism, the intro line I love for its blunt to-the-pointness. We should co-opt it for here. Dysmorodrepanis 22:41, 23 August 2007 (UTC)
Who says we're not going to cover genetic polymorphism? Not me, for sure. Genetic polymorphism is a type of phenotypic polymorphism; all polymorphism (but not all variation, note) is heritable, partly or wholly. I just wanted to stay on the phenotype side of the great phenotype/genotype divide. We are having enough trouble as it is! When you talk of SNPs &c you are talking about the genotype. Macdonald-ross 13:33, 24 August 2007 (UTC)
I meant "If we're not going to cover genotypic polymorphisms". Sorry to be unclear. —JerryFriedman 22:08, 27 August 2007 (UTC)

Are opposing selection pressures really usually "powerful"? I'd think that in a lot of obvious cases, such as blood types or human eye color or the jaguar fur color mentioned in the article, the selection pressures are pretty weak.

They need to be powerful for polymorphism to gain an evolutionary trajectory. I.e., a stable polymorphism is at equilibrium regarding selective forces. Not for the individual, but for the population gene pool. Dysmorodrepanis 22:41, 23 August 2007 (UTC)
Are there really powerful selection pressures on human eye color, or a personal favorite of mine, deuteranomaly? It seems to me that a balance of weak selection pressures or no pressure at all could maintain polymorphism. —JerryFriedman 22:01, 27 August 2007 (UTC)
Deuteranomaly - now that's an idea for a userbox... Anyways, point in case I'd say. There is no strong selection against or for, hence it's roughly at equilibrium. As opposed to rod monochromacy which would not be as easy to shrug off, except when it's common and widespread (locally) as a result of drift. But that is also at about equilibrium level ('cause it's an old polymorphism), but, due to being quite more of a disadvantage, at a lower incidence except on Pingelap. Dysmorodrepanis 02:46, 7 September 2007 (UTC)

I don't get what you're driving at in the new paragraph in the Ecology section. I'm not sure what the sentences have to do with each other, and it looks like it's saying that heterozygote advantage is the only cause of polymorphism. But what about flexibility, where the different phenotypes have advantages in different situations? —JerryFriedman 22:01, 23 August 2007 (UTC)

The original short para was quite wrong to say:
"The segregation of a population into morphs, especially if the morphs are, or become, reproductively isolated, could be thought of as a precursor to sympatric speciation."
The populations we are discussing are not segregated! Nor isolated, reproductively or otherwise. The morphs are all part of an interbreeding group, their phenotypes show discrete variations (that's why they got studied). So the issue of sympatry or otherwise is irrelevant. Of course, at any time, populations could become isolated, but that's another story.
The original paragraph was from the former article "Morph (zoology)" and was about the two fish examples in the present article, in which the morphs still interbreed, but show some assortation. (In the Arctic char example but not the brown trout example, they also segregate spatially.)
Also, the article needs to mention frequency-dependent selection. Also, what's the word for the mosquito example in the article? The two phenotypes have advantages in different situations (different weather). That doesn't seem to be either heterozygotic selection or frequency-dependent selection. —JerryFriedman 22:01, 27 August 2007 (UTC)
I'm afraid the first para also needs changing; 'organisms of different types' is deeply ambiguous; remember that polymorphism is not a synonym for variation, and that the definitions in the intro now come close to standard usage. Macdonald-ross 12:42, 24 August 2007 (UTC)

[edit] Examples of polymorphisms

Here we can collect papers about biological polymorphism, to use as references. You can find case examples easily by searching for "polymorph" and "animalia" ("plant", "aves", ...) on Wikipedia.

[edit] Free fulltext available

  • Biol. J. Linn. Soc. 88: 475: Linkage disequilibrium between a melanin-based colour polymorphism and tail length in the barn owl. [1]
  • Biol. Rev. 79: The evolution, maintenance and adaptive function of genetic colour polymorphism in birds [2]
  • Evol. Ecol. Res. 7: 303: Trophic morphology, feeding performance and prey use in the polymorphic fish Herichthys minckleyi PDF
  • Heredity: 92: 156: Extreme polymorphism in a Y-linked sexually selected trait PDF
  • PNAS 98: 8985: A polymorphic dinucleotide repeat in the rat nucleolin gene forms Z-DNA and inhibits promoter activity PDF
Might be discussed in some of the DNA articles. The structural polymorphism is outside this article's scope, but the underlying dinucleoitide repeat polymorphism may be in.
  • PNAS 101: 9009: Early events in speciation: Polymorphism for hybrid male sterility in Drosophila PDF

[edit] Other/Not checked

Free fulltexts may be available on authors' pages, journal Web sites, Google Scholar "All Versions", etc

  • Biol. J. Linn. Soc. 61: 369: Novel colour polymorphisms in a hybrid zone of Mandarina (Gastropoda: Pulmonata)
  • Biol. J. Linn. Soc. 86: 265: Asymmetric reproductive isolation among polymorphic salamanders
  • Biotropica 6: 205: Adaptive Polymorphism Associated with Multiple Müllerian Mimicry in Heliconius numata (Lepid., Nymph.)
  • Biology Letters 3: 169–172: Right-handed snakes: convergent evolution of asymmetry for functional specialization doi:10.1098/rsbl.2006.0600 [predator-driven maintenance of stable polymorphism]
  • Ecology 84: 1441: Trophic polymorphism and behavioral differences decrease intra-specific competition in a cichlid, Herichthys minckleyi
  • J. Ecol. 89: 749: Ecology of Fruit-Color Polymorphism in Myrtus communis and Differential Effects of Birds and Mammals on Seed Germination and Seedling Growth
  • Green, DM, CW Zeyl & TF Sharbel. 1993. The evolution of hypervariable sex and supernumerary (B) chromosomes in the relict New Zealand frog, Leiopelma hochstetteri. J. Evol. Biol. 6: 417:
This is one paper that absolutely has to be in here eventually. Whoever can grab it, read it. This is too weird shite not to present to the public at large. Dysmorodrepanis 23:06, 23 August 2007 (UTC)

The folowing comes from the blog page of Christopher Taylor on blogger.com, so don't go putting it on the main article!! I've interspersed some thoughts which illustrate how even such an exciting example is probably not right for the article. Macdonald-ross 12:47, 27 September 2007 (UTC)

"The strange relictual frog genus Leiopelma (the species Leiopelma archeyi is shown in a photo from the page of Dr. Bruce Waldman).

"Leiopelma is a small genus of four living species restricted to New Zealand. They represent a basal grade of frogs of which the only other member is the "tailed frog" Ascaphus truei from western North America. Leiopelma and Ascaphus retain a number of primitive features that have been lost in other frogs, such nine vertebrae in front of the sacrum and tail-wagging muscles (though the 'tail' of male Ascaphus is actually the copulatory organ). Leiopelma also lack a tadpole stage in their life-cycle, hatching straight out into froglets.

"Of the four species living today, at least three have different methods of sex determination from each other. And within two of those species, there are even different populations that differ in their mode of sex determination!

"The most primitive state is perhaps that shown by Leiopelma archeyi, in which most populations don't have distinguishable sex chromosomes. This is the condition in most amphibians, though it has been shown that even in taxa that don't have heteromorphic chromosomes, sex is still determined genetically (Hayes, 1998). However, a heteromorphic W sex chromosome has been recorded in one population of L. archeyi from Whareorino in the King Country (Green, 2002). [ie a geographical race Macdonald-ross] In other features (including genetic features) the Whareorino L. archeyi are almost indistinguishable from Coromandel populations that lack the W chromosome.

"The Whareorino Leiopelma archeyi are therefore more like L. pakeka in sex differentiation. Leiopelma pakeka also has a female-ZW/male-ZZ set-up (Green, 1988). There is only a single population of L. pakeka, restricted to Maud Island, which doesn't give much scope for variation [Oh, yes it does! see main article Macdonald-ross].

"The species Leiopelma pakeka was recognised only recently (Bell et al., 1998). Previously it had been regarded as a population of the genetically distinct but morphologically almost identical L. hamiltoni, and its genetic structure was described under the latter name. Leiopelma hamiltoni proper is uber-rare, with a population of less than 300 individuals restricted to less than one hectare of habitat on Stephens Island, and does not seem to have yet been investigated for sex chromosomes. [either geographical races or distinct species Macdonald-ross 12:47, 27 September 2007 (UTC)]

"The ultimate wierdness, however, comes when we look at Leiopelma hochstetteri. Most populations of L. hochstetteri have a single sex chromosome in females, while males lack a sex chromosome. This female-0W/male-00 system is unique - no other animal has it. Not one. In fact, it's so bizarre that not even all L. hochstetteri have it - females of the population on Great Barrier Island lack the lonely W chromosome [geog. var. again. Macdonald-ross], and like Coromandel L. archeyi this population does not have morphologically distinct sex chromosomes (Green, 1994). The Great Barrier population also lacks the non-sex-related supernumerary chromosomes (or "B" chromosomes) found in other populations (Green et al., 1993). B chromosomes are small, seemingly dispensable chromosomes that are found in a broad scattering of taxa. In species where they are found, numbers of B chromosomes can vary significantly within and between populations, probably because their lack of significant function means a lack of selective control on their propagation [if a genuine polymorphism then selection highly likely to be acting. Macdonald-ross]. This variation is also seen in L. hochstetteri, where up to 15 B chromosomes were found in individuals of five different populations [this could be a genuine polymorphism: needs further research. Macdonald-ross]. The variation in chromosomes between populations is shown below in a figure from Green (1994).

"So how did all this come about? I am not aware of any other group of closely-related organisms showing this much variation in so few species. However, it is possible to imagine ZW chromosomes evolving through differentiation of morphologically indistinct sex-determining chromosomes, and this is what appears to have occurred in Leiopelma pakeka and Whareorino L. archeyi. Leiopelma hamiltoni appears to be more closely related to L. archeyi than L. pakeka (Bell et al., 1998), so it would be very interesting to know whether or not it has distinct sex chromosomes.

"As for Leiopelma hochstetteri, the sister taxon to all other Leiopelma, phylogenetic analysis of chromosome characters shows that the Great Barrier population, without the extra W chromosome, is probably sister to all other populations. Green et al. (1993) suggest that the 0W/00 system could evolved from a ZW/ZZ system. Either the Z chromosome may have been lost, or (as the authors of the latter study think more likely) it could have been duplicated, giving a ZZW/ZZ pattern that would be karyotypically indistinguishable from 0W/00."

REFERENCES

Bell, B. D., C. H. Daugherty & J. M. Hay. 1998. Leiopelma pakeka, n. sp. (Anura: Leiopelmatidae), a cryptic species of frog from Maud Island, New Zealand, and a reassessment of the conservation status of L. hamiltoni from Stephens Island. Journal of the Royal Society of New Zealand 28 (1): 39-54.

Green, D. M. 1988. Heteromorphic sex chromosomes in the rare and primitive frog Leiopelma hamiltoni from New Zealand. Journal of Heredity 79 (3): 165-169.

Green, D. M. 1994. Genetic and cytogenetic diversity in Hochstetter's frog, Leiopelma hochstetteri, and its importance for conservation management. New Zealand Journal of Zoology 21: 417-424.

Green, D. M. 2002. Chromosome polymorphism in Archey's frog (Leiopelma archeyi) from New Zealand. Copeia 2002 (1): 204-207.

Green, D. M., & D. C. Cannatella. 1993. Phylogenetic significance of the amphicoelous frogs, Ascaphidae and Leiopelmatidae. Ecol. Ethol. Evol. 5: 233-245.

Green, D. M., C. W. Zeyl & T. F. Sharbel. 1993. The evolution of hypervariable sex and supernumerary (B) chromosomes in the relict New Zealand frog, Leiopelma hochstetteri. Journal of Evolutionary Biology 6 (3): 417-441.

Hay, J. M., I. Ruvinsky, S. B. Hedges & L. R. Maxson. 1995. Phylogenetic relationships of amphibian families inferred from DNA sequences of mitochondrial 12S and 16S ribosomal RNA genes. Molecular Biology and Evolution 12 (5): 928-937.

Hayes, T. B. 1998. Sex determination and primary sex differentiation in amphibians: Genetic and developmental mechanisms. Journal of Experimental Zoology 281 (5): 373-399.

[end of excerpt. Macdonald-ross 12:47, 27 September 2007 (UTC)]

  • J. Roy. Soc. New. Zeal. 33: 715: Phylogeographic genetic analysis of the alpine weta, Hemideina maori: evolution of a colour polymorphism and origins of a hybrid zone
  • New. Zeal. J. Zool. 22: 393: Hybridisation of tree weta on Banks Peninsula, New Zealand, and colour polymorphism within Hemideina ricta (Orthoptera: Stenopelmatidae)
  • J. Zool. 245: 245: Polymorphism, mating preferences and sexual selection in the Arctic Skua
  • Proc. Roy. Soc. B 175: 255: Polymorphism and Behaviour in the Arctic Skua (Stercorarius parasiticus (L))
  • J. Zool. 249: 411: Plumage polymorphism of red-footed boobies (Sula sula) in the western Indian Ocean: an indicator of biogeographic isolation.
  • J. Zool. 264: 391: Pigmentation polymorphism in the invasive amphipod Dikerogammarus villosus: some insights into its maintenance
Dikerogammarus villosus ought to get an article BTW. I won't tough them, they're mere duck food. But I hear the name quite often these days.

Web extract of above paper is presented below:

"Pigmentation polymorphism in the invasive amphipod Dikerogammarus villosus: some insights into its maintenance

S. Devin a1c1, L. Bollache a2, J.-N. Beisel a1, J.-C. Moreteau a1 and M.-J. Perrot-Minnot a2

a1 Laboratoire Biodiversité et Fonctionnement des Ecosystèmes (LBFE), Université de Metz, Campus Bridoux, Avenue du Général Delestraint, 57070 Metz, France a2 Equipe Ecologie Evolutive, UMR CNRS 5561 Biogéosciences, Université de Bourgogne, 6 boulevard Gabriel, 21000 Dijon, France

Abstract

Dikerogammarus villosus, a freshwater invasive amphipod, exhibits conspicuous pigmentation polymorphism. This polymorphism is documented in two recently colonized areas, the Saône and Moselle rivers (north-eastern France), and some of the mechanisms by which pigmentation polymorphism can arise and be maintained are addressed. Body size, reproductive status, fecundity and mate choice are compared among morphs of D. villosus in field samples collected in summer 2001. Body size and female gonad developmental stage were comparable among the different morphs, suggesting that polymorphism is not the result of changes in pigmentation with age or moult-cycle. Fecundity and reproductive status (paired vs non-paired) were not affected by pigmentation morph either. A random combination of morphs in pre-copula pairs was observed, showing that the colour pattern does not play a major role in mate choice. A strong size-assortative pairing was found, and this pattern was similar among male morphs. Overall, our study shows that morph polymorphism is not related to different stages in the moult cycle or the life cycle, and is not maintained by morph-assortative pairing. Alternative explanations to the mate choice hypothesis for the maintenance of pigmentation polymorphism are discussed." [my comment is as follows: this is a genuine example of p/morphism, but it is quite undeveloped in research terms, and does not compare well with the examples in the article. In particular, how the morphism relates to the ecology is not known, and how it is maintained genetically or otherwise is not known. Macdonald-ross 13:07, 27 September 2007 (UTC)]


  • Nature 378: 95: Genetic Polymorphism for Alternate Mating Behaviour in Lekking Male Ruff Philomachus pugnax
A classic.
  • New Zeal. J. Zool. 21: 417: Genetic and cytogenetic diversity in Hochstetter's frog, Leiopelma hochstetteri, and its importance for conservation management
  • Science 243 643: A Diet-Induced Developmental Polymorphism in a Caterpillar

[edit] Wikipedia articles

  • RFLP - technique based on genetic polymorphism due to point mutation. Latter if it survives for generations results in a new allele can be significant in evolution (sickle cell hemoglobin, melanin production y/n etc)
  • Genetic fingerprinting - utilizes genetic polymorphism that is of little evolutionary significane if at all.
  • Chromosomal polymorphism

[edit] Other examples

Polymorphisms in the scarlet tiger moth and in the African swallowtail Papilio dardanus (in which one of the eight races has 13 morphs)[1] have been the subjects of considerable ecological and genetic study.

The predatory mosquito Chaoborus americanus has two larval morphs, one large, yellow, and quick to develop; the other small, pale, and slow to develop. The larvae overwinter, and the polymorphism is an adaptation to unpredictable spring weather. The fast-developing larvae do well in warm springs, but die off in springtime freezes, whereas the slow-developing ones do well in springs with freezes. Many other insects with polymorphisms in development and dormancy are known.[2]

A possible example of behavioral polymorphism is that anadromous individuals of brown trout (Salmo trutta morpha trutta) may occur sympatrically with a stream-resident ones (Salmo trutta morpha fario). The two morphs are part of the same species and may interbreed [3]; are they polymorphic?. To be accepted as polymorphic it is essential that they are part of the same interbreeding population; otherwise they must be considered as parapatric variants. Frequently, the likelihood of interbreeding is reduced because the morphs also have distinct reproductive behaviours such as variance in timing or in the selection of sites for reproduction; this argues for parapatric geographical variation.

The segregation of a species into sympatric morphs often can be thought of as a mechanism for the partitioning of available resources. An example of this might be certain lacustrine Arctic char populations which segregate into planktivorous and piscivorous morphs within the same lake. However, this example is probably also parapatric variation rather than true polymorphism.

Other polymorphisms are detectable only in the laboratory. An example is that several enzymes (e.g., phosphoglucomutase) taken from different individuals move with different speeds when exposed to an electric field (electrophoresis).

[edit] Questions in the article

Why are there questions in the article? Encyclopedias provide answers not questions. The article needs a rewrite. 83.147.180.185 20:45, 6 September 2007 (UTC)

Look at this page. The rewrite is in full swing. You should have seen this... thing... half a year ago! ;-) Dysmorodrepanis 02:47, 7 September 2007 (UTC)


[edit] Intro clarification

When I wrote 'Polymorphism is both caused and modified by selection', this got changed to eliminate the 'caused'. So I've tried to make it clear. First, polymorphism doesn't just happen; it comes about by means of natural selection because of its fitness in the given ecological situation. The existence of genetic features like strong linkage between alleles (super-genes) is no accident! It reveals the existence of previous selection in favour of the polymorphism.

Now, I don't want to say all this in an intro, but I do want to convey the idea that the existence of polymorphism in a species is no accident. Hence the present wording. I'm open to comments from regular readers; some of this is difficult stuff, and took some very bright people much of their careers to figure out. So, as on many science articles, we want to be understood, whilst nevertheless being accurate. Macdonald-ross 16:11, 11 September 2007 (UTC)

[edit] Some restructuring required

Hi, firstly I'm gratified that this article is developing and I offer my encouragement to the contributing editors to keep up the good work.

As a non-specialist in the field, I would expect the lead to give an over view, and subsequent sections to give expansion of details. This doesnt seem to be the case.

Also I feel if you want to have a section titled What polymorphism is not, it should be preceded by a section titled What polymorphism is which lays down the basis of polymorphism in greater detail than the lead and also points towards the sections which follow on additional subtopics. After this section, you may have the section on What polymorphism is not or it may be placed after the additional subtopics are dealt with.

A logical structure would help the article, which is difficult to comprehend exactly for the lay reader, become easier to understand.

AshLin 15:42, 18 September 2007 (UTC)


  • Well, thank you for the comments. A general reader is indeed entitled to some straightforward statements that make it clear what the page is about, and I've rewitten the first few paras with that in mind. I have been rather buried in the examples, too much, perhaps.
  • At the same time, the page does need to use terminology from genetics and evolutionary studies, though, naturally, as little as we can get away with. The history of the discussion before the present editing suggested that the 'What polymorphism is not' section was very much needed before we get to the examples.
  • The heart of the page is really in the examples, which are brief summaries of some fascinating situations. They might tempt readers to investigate further, and even to take a closer look at nature in the wild!
  • You don't mention the really strange thing about this page is its location in Medicine and Cell & Molecular Biology, neither of which is really central to the content!! There is going to be something on chromosome polymorphism, which hopefully will keep the cell biologists happy; and I suppose one could make a huge list of human polymorphisms...

Macdonald-ross 15:34, 19 September 2007 (UTC)

[edit] Tidying up

I've moved the Other Examples section in the Main page to this Talk page. This is not a judgement that we should have no more examples, but a recognition that as they were these examples were not suitably developed, and some were probably not for this page. Macdonald-ross 15:19, 24 September 2007 (UTC)

[edit] Genes and phenes, again

There is a recent book on the topic of natural variation and polymorphisms, which serves to show that no strict dividing line between genetic and phenotypic polymorphisms can be drawn and how every polymorphism has an underlying molecular component, whether that is "genetic" in the strict sense (= hereditary), genetically imprinted during development (= inborn but not inherited) or flexibly adapted during an organism's life (oystercatcher billtip morphology - the "probing", "chiseling" and "cutting" phenotypes) which are not genetical in the strict sense but have their underlying metabolical - and ultimately genetical - pathway.

The book is:

Benedikt Hallgrímsson and Brian K. Hall, editors (2005): Variation – A Central Concept in Biology. Elsevier Academic Press, Burlington. ISBN 0-12-088777-0 http://www.elsevier.com/wps/find/bookdescription.cws_home/705523/description

Dysmorodrepanis (talk) 15:51, 16 January 2008 (UTC)

Thanks for the ref; I agree with the two editors that variation is a central concept in biology. But I'm not quite sure what your point is; paras 4 and 5 of the intro do say clearly that polymorphism has a genetic basis.
There is certainly a place for other articles not at present in WP: an obvious example is
Variation (biology) -- which redirects to a disambiguation, but not to a substantive article
This present article is in a fairly stable condition; it does what it says on the tin (the intro) and it is supported by more than adequate references. Which is more than can be said for most articles! Macdonald-ross (talk) 17:54, 16 January 2008 (UTC)
Yes, I noted. It has been good work, a major effort. The issue had been disputed initially (how much genetics should be in), so I just wanted to mention this source because it could wrap up some points. Content is stable, someone might go over it cpyediting it for style and consistency and it might even be suggested for GA. I certainly would not call it B-class anymore. What do you think? Dysmorodrepanis (talk) 20:11, 16 January 2008 (UTC)

Well; that's a thought. I'm not sure I really know the procedure; I have noticed that articles seem to get stuck on 'B' and never seem to get to 'A'! GA is maybe what people go for. How does one go about it? Macdonald-ross (talk) 21:49, 16 January 2008 (UTC)

The only thing I've done is ask at the relevant project's talk page for a rerating. And I've done that only once or twice, for bird articles, so I don't know how it will work for the projects that have rated this article. —JerryFriedman (Talk) 17:59, 22 January 2008 (UTC)
Wait, I think I misunderstood you as looking for an A rating. For the GA procedure go to Wikipedia:Good_article_nominations, which will direct you first to Wikipedia:Good_article_criteria. —JerryFriedman (Talk) 18:04, 22 January 2008 (UTC)

[edit] Comment on DNA polymorphisms

As explained earlier, this page should not try extend itself to cover DNA morphism.

1 because that breaks the phenotype/genotype conceptual boundary.
2 because this article is mostly about visible morphism.
3 because this article is already overfull.

DNA morphism deserves a separate article, and I urge molecular guys to set it up (already SNPs and RFLPs have articles). Don't put DNA concepts into this article, which is now coherent and sufficient! Macdonald-ross (talk) 13:17, 22 January 2008 (UTC)

In that case this article might need a different name, as DNA polymorphisms are certainly part of biology. What would be a better name? —JerryFriedman (Talk) 17:56, 22 January 2008 (UTC)
The p/m (biology) was just a way of disambiguating, nothing more; but I can appreciate it may cause the thought of SNPs to cross users' minds! The article's content comes mostly from ecological genetics. I'm in favour of DNA p/m having a place in biology WP, why not an article of its own? To try and do the DNA p/m at the same time would a) make the article more difficult to comprehend, b) make the loading and editing slower and more unwieldy.
Renaming is a good idea, I think. I would rather see the page called, for instance, Polymorphism (ecogenetics) than have it grow even more complex. We could do that just by moving it to the new title. How does that strike you? Macdonald-ross (talk) 18:33, 22 January 2008 (UTC)
I think I'd prefer Polymorphism (ecology and genetics) as using more familiar words. Otherwise it sounds like a good plan. Maybe there should be a "polymorphism (biology)" disambiguation, or maybe this should be handled on the present disambiguation page. —Preceding unsigned comment added by JerryFriedman (talk • contribs) 21:02, 22 January 2008 (UTC)
This written before your comment arrived: Other titles might be considered: morphism instead of polymorphism, or ecology instead of ecogenetics. The content overlaps with the balancing selection stub, which is in poor shape; somehow that title emphasises the abstract (selection} instead of the concrete (polymorphism). Macdonald-ross (talk) 21:14, 22 January 2008 (UTC)
Your Polymorphism (ecology and genetics) has the advantage of describing the contents accurately, but it's a handful to type out every time someone wants to refer to it, or a user to search for it. Macdonald-ross (talk) 21:19, 22 January 2008 (UTC)

[edit] Heterogenous / heterogeneous

These spelling alternatives can be irritating, but here is the thing: both spellings are correct, both are accepted in major dictionaries. The word has two roots: hetero- (= different) and gen(e)ous (= type). The second part is the same root as genus, and I think simplicity requires we go for the shorter word, which is also easier to pronounce. Macdonald-ross (talk) 15:15, 26 February 2008 (UTC)