Talk:Dominance (genetics)/Archive 2

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Recessive genes, recessive alleles, recessive traits...

Can these terms be used interchangably? From what I understand, there's no such thing as a "dominant/recessive gene", only a dominant allele. Please correct me if I am wrong. --123.243.7.17 (talk) 07:44, 23 February 2009 (UTC)

Many scientists use these terms interchangeably, although technically speaking, only traits are dominant/recessive. On the DNA level, all alleles of all genes act in an additive way without any dominance being present. An allele may be dominant/recessive for one trait, but not for another. An example is the albino allele, c. The albino trait is recessive as Cc individuals are pigmented. However, if you look at the underlying enzyme defect, Cc individuals are intermediate between CC and cc opnes for tyrosinase activity. So for the character "tyrosinase activity" dominance is absent, for the character "pigmentation" albino is recessive to pigmented. --Crusio (talk) 09:11, 23 February 2009 (UTC)

Thank you. However, shouldn't the article be updated to be consistent? --123.243.7.17 (talk) 09:27, 23 February 2009 (UTC)

The three terms most definitely cannot be used interchangeably, and no scientist or anybody else interested in accuracy does so. Only alleles are dominant or recessive, and this is merely a shorthand way of talking about their effects on particular aspects of phenotype. There is no such thing as a recessive 'gene', only a recessive form (allele) of the gene, though this error is so common in popular culture that one has to deal with it. Likewise, traits themselves are neither dominant nor recessive: one might talk about 'the recessive trait' as being the one produced by two recessive alleles (aa), and 'the dominant trait' as the one produced by two dominant alleles (AA) or one dominant and one recessive (Aa). One might also say in 1867 "the wrinkled trait is inherited as a recessive," which is inaccurate but interpretable in 2009 as "if a pea plant inherits two alleles [but not one only] at the starch-branching protein gene locus that produce a form of SBP unable to maintain turgor pressure, its seeds will be unable to retain water and will show a wrinkled phenotype." That is: there is no gene 'for' wrinkled, the trait itself is not inherited (the DNA is), and we call it 'recessive' as a shorthand for two but not one allele like that. Alleles are co-dominant at the DNA level, since both are present as DNA sequences (and may be detected as such), and are often but not always additive, as for example when 'null' alleles contribute no protein product at all to phenotype formation. The discussion of tyrosinase is sufficiently accurate, except again for the confusion of dominant or recessive 'traits'(Smcewincarr (talk) 17:28, 14 October 2009 (UTC))

I don't think that Crusio is confused at all. Your statement that "only alleles are dominant or recessive" is, at the very least, an overstatement. What about sickle-cell anemia? Generally speaking, having two copies of the responsible beta-globin allele causes full-blown anemia, but having one copy does not. So it's a recessive allele. At the same time, having only one copy DOES cause one to have sickle-cell trait, which includes some risks and symptoms and also some malaria resistance. If we look chiefly at those traits, the responsible allele is dominant! As you almost certainly know, as you're clearly well-informed enough to be confidently incorrect, real alleles have pleiotropic, dose-dependent effects. If you don't accept that the terms "dominant" and "recessive" describe how traits arise from combinations of alleles, rather than to the individual alleles themselves, then the terms are obsolete and only good for confusing first-years. —Preceding unsigned comment added by 130.212.157.68 (talk) 01:41, 12 November 2010 (UTC)

Please note that I said "only alleles are dominant or recessive", not "all alleles are dominant or recessive," by which I meant that traits are dominant or recessive only insofar as they are produced by dominant or recessive alleles. As noted, this usage is supported by the standard Dictionary of Genetics, and all three of the genetics textbooks I have used since 1997. Re sickle-cell, the general health of AS heterozygote (with 'sickle cell trait') more nearly resembles the standard AA homozygote than the SS homozygotes (with 'sickle cell anemia'), hence full-blown anemia is called a "recessive disease,", as in OMIM. If you wanted to call any degree of anemia a trait, then the AS and SS show that trait and AA doesn't, so S would be dominant: of course, nobody says that. As classically taught ('peas first, DNA later'), "dominant" and "recessive" are indeed confusing, precisely because students assume they are intrinsic properties, especially that 'recessive' is synonymous with mutated, rare, odd, deleterious, disease-causing, etc. An alternative is to describe the molecular basis of genetic disease first, and then introduce the terms as shorthand for descriptions of interactions. That's what I've done here. cf [1], starting with second half. Smcewincarr (talk) 02:13, 28 December 2010 (UTC)

"one dominant and one recessive (aa)" -- I assume you mean "one dominant and one recessive (Aa)", no? Emw (talk) 17:56, 14 October 2009 (UTC)
Correct, and corrected above (Smcewincarr (talk) 18:44, 14 October 2009 (UTC))

Images

I see there is a request for diagrams, and was surprised not to find any in the article already how about the following as a starter: L∴V 12:25, 17 August 2009 (UTC)

I understand this article to be about Dominance per se, and not about Genetics generally or pedigree analysis in particular. Hence, I don't think this diagram is necessary. Smcewincarr (talk) 16:39, 27 December 2010 (UTC)

Disputed tag

I have placed a "disputed" tag on the article because, although many scientists speak about "dominant" or "recessive alleles", technically speaking, only traits are dominant/recessive. On the DNA level, all alleles of all genes act in an additive way without any dominance being present. An allele may be dominant/recessive for one trait, but not for another. An example is the albino allele, c. The albino trait is recessive as Cc individuals are pigmented. However, if you look at the underlying enzyme defect, Cc individuals are intermediate between CC and cc ones for tyrosinase activity. So for the character "tyrosinase activity" dominance is absent, but for the character "pigmentation" albino is recessive to pigmented. --Crusio (talk) 12:41, 27 August 2009 (UTC)
Good point. Why don't you add this explanation as a caveat to the more traditional basic one about appearance presented here and remove the tag? Peace Earthdirt (talk) 00:59, 23 September 2009 (UTC)

Well, because the "more traditional basic one" is the one I described above. The view presented in the article is an unfortunate shorthand that is incorrect... And I don't have the time to re-write the whole article. --Crusio (talk) 07:56, 23 September 2009 (UTC)

There is no dispute: only alleles, never traits, are dominant or recessive. The "more traditional basic one" is pre-molecular, outdated, and confusing to modern students. Mendel himself occasionally confuses inheritance of the trait with inheritance of the factor causing the trait. As above, if you said 'wrinkled is a recessive trait in peas', I would know what you think you mean, but would dock points on an exam for confusing genotypes (inherited) with phenotypes (not).

I didn't have time to re-write the whole article either, but did so anyway. I will shortly have to go back and re-correct the error that Sickle-Cell shows 'incomplete' dominance —Preceding unsigned comment added by Smcewincarr (talk • contribs) 17:37, 14 October 2009 (UTC)

I beg to differ. You may deduct points from your students' exams, but if they submit a paper to my journal using this kind of terminology, I'll slap them on their fingers (if I see it in time, of course :-)... :-) Just one citation here: Gregor Mendel stated (as cited by Reeve, Encyclopedia of Genetics, p. 63): "The dominant character can have ..." No need to continue. Mendel defined dominance, without knowing anything about genes of alleles. He talked about characters (what we now call phenotypes). Perhaps this is the "pre-molecular outdated view". But the tyrosinase example I give above clearly demonstrates the problem. Neither of the alleles is dominant or recessive. As you yourself said above, on the DNA-level all alleles are co-dominant. Yep, in that case the DNA sequence itself is the trait being studied. Which one of the tyrosinase alleles is dominant, C or c?? If you study coat color, it's C, obviously. If you study tyrosinase activity, there is no dominance and inheritance is purely additive. Looking at DNA sequences, there is co-dominance. It all depends on what trait you are looking at. Looking at coat color, it clearly would not make any sense to say that there is co-dominance, etc. --Crusio (talk) 18:44, 14 October 2009 (UTC)

To begin resolving this dispute, I think it would be helpful to find in a textbook whether dominance refers to traits or alleles. Supporting whatever claim is thus made can be done best through inline citations. Emw (talk) 18:26, 14 October 2009 (UTC)

Part of the problem is that this sloppy usage has become so pervasive. I bet you'll find textbooks stating that such and such knockout mouse "did not have a phenotype"... --Crusio (talk) 18:45, 14 October 2009 (UTC)

King's definition, just added to the article by Smcewincarr, is an example of this sloppy thinking: "dominance [refers] to alleles that fully manifest their phenotype when present in the heterozygous ... state". Apply this to the tyrosinase example above. Obviously, whether you call C dominant or not depends on which phenotypical trait you are looking at. --Crusio (talk) 18:50, 14 October 2009 (UTC)

I will go round with thee, fellow. *My* journal deals with mtDNA, so I don't have to worry about dominance:) In essence we agree, the tyrosinase example showing that this is almost entirely semantic. You say 'no dominance', I say 'incomplete dominance' which avoids the implication of 'no interaction.' Coat color would clearly be co-dominant, if the two alleles produced eumelanin and phaeomelanin patches rather than a uniform orangey-black mixed pigment, but at what level patchy can be distinguished from essentially uniform is undefined. Mendel talked about 'unit factors' and recognized 'round factors' and 'wrinkled factors,' (clearly anticipating alleleic interaction) and occasionally confuses factors with traits, in the absence of knowledge about DNA, which is no more a disgrace than Darwin getting it wrong about Natural Selection in the absence of knowledge of the General Selection Model.

King et al is an authoritative modern dictionary of genetics, and defines dominance in terms of alleles, as added to the entry. Griffiths et al., Klug & Cummings, Snustad & Simmons *all* define dominance in terms of alleles, to grab the first three that come to hand. I'll quote ten more if you like...

My degree is in Genetics, from a Department of Genetics, and I teach Genetics, and it pains me to acknowledge that I can teach all about PKU without once having to say recessive or dominant, except to show why OMIM uses those terms. Human geneticists will also talk about dominant and recessive 'genes,' even where I'm a co-author and get outvoted by my fellows and the editor. (Smcewincarr (talk) 19:22, 14 October 2009 (UTC))

Well, fellow, my degree is in Zoology, from a Department of Zoology and all I ever taught for a couple of years was Animal Physiology, how's that!

Mmm, doesn't sound too convincing for this discussion, actually :-) Seriously, you're absolutely right. We're talking semantics here. By the way, the C gene I am talking about is the albino gene, so c produces no pigment whatsoever. So that's not co-dominant. As for incomplete dominance, my original training was as a quantitative geneticist. I express characters as numerical values. If Aa is exactly between AA and aa, I say "no dominance, purely additive", if Aa equals AA or aa (in QG the allele that increases the value of the trait is written as capital letter), I say "complete dominance for high or for low, respectively", if Aa is in between AA and aa (but not exactly in the middle), that's "incomplete dominance", and if Aa is beyond the range of AA-aa, that is "overdominance".

However, semantics is important. If you have access to the journal, read this (doi:10.1016/j.biopsych.2003.12.026), it has some amusing anecdotes (first paragraph) on what happens when people don't understand each others terminology any more (and tells of an interesting concept of "dominance", by the way). As you say, sometimes co-authors and editors impose incorrect terminology on you. I try to resist this trend, though, although I'm sure there must be dozens of examples from "my" journal where I failed... My point is, in a number of years, if your co-authors or those editors start writing textbooks, they'll probably write about dominant or recessive genes. Are you going to abide with that? --Crusio (talk) 20:16, 14 October 2009 (UTC)

Returning to this 'factual dispute' after a year or so, I take the accuracy of the article's definition of dominance in terms of alleles to be settled. Does this flag get removed? Smcewincarr (talk) 16:54, 27 December 2010 (UTC)

Complete dominance

Complete dominance is described on the page as "the phenotype of the heterozygote is completely indistinguishable from that of the dominant homozygote". I feel this is incorrect as complete dominance describes the condition when in the heterozygous state, the dominant allele completely masks the effect of the recessive allele. —Preceding unsigned comment added by 144.82.216.201 (talk) 05:01, 22 January 2010 (UTC)

Isn't that the same? If the het matches the phenotype of one of the homs, you don't see any effect of the recessive allele. --Crusio (talk) 07:36, 22 January 2010 (UTC)

It's the same in practice, and the way it's currently phrased is more accurate. The idea of the dominant allele "masking" the other's effect doesn't really correspond very well to actual mechanisms of dominance. The definition should be stated in terms of the observable phenotype, and that's what the current one ("the phenotype of the heterozygote is completely indistinguishable from that of the dominant homozygote") does. Agathman (talk) 15:25, 22 January 2010 (UTC)

Apologies everyone, it must have been a very late night. Looking back, both do mean essentially the same thing and suggestion noted. —Preceding unsigned comment added by 144.82.216.201 (talk) 14:35, 26 January 2010 (UTC)

Proposed de-consolidation

There needs to be a separate article for "autosomal Dominant". It is absolutely ridiculous to include it under the "dominance" article. In short, this article is terrible an needs a lot of work. For those of you who want to avoid reading these tedious arguments below, please read a new article in the Journal of Pathology that brilliantly summarizes these debates below. This article should be the basis of the dominance article (Dominance and gene dosage balance in health and disease: why levels matter, from the journal of pathology (PMID=19827001). 14:59, 4 March 2010 (UTC)

I don't really see why autosomal dominant should not be part of the article on dominance. As for the article you mention (I have slightly edited your comment - we don't usually use reference tags on a talk page), Fig. unfortunately starts of with an incorrect definition of co-dominance... --Crusio (talk) 15:34, 4 March 2010 (UTC)
For starters, there is an article on X-linked recessive inheritance, Autosomal recessive, but not one on Autosomal Dominant human diseases. In the past you suggested having a separate list of autosomal dominant conditions, what changed? The dominance article includes almost no reference to diseases caused by autosomal 'dominant' mutations which is what the majority of . The definition of "dominence" listed is the most ambiguous description possible.. "its a relationship between two alleles at a locus". The abstract and simplified concept of dominance is entirely absent from this article. The article immediately jumps to discussing very unnecessarily detailed examples of why dominance isn't so concrete before laying out what dominance is in classical terms. The 'human disease dominant' section is a convoluted discussion on PKU and contains the only graph in the whole article. If your going to revert any changes that try to explain dominant genetics in abstract terms that are fully cited and would be useful to readers, then you need to allow for the creation of an article on "autosomal dominant" human mutations so us in medicine can have a place to point people to learn about genetics. Instead, your using this as a mouthpiece for your journals semantics on dominance. Its wholly inappropriate.UberMD (talk) 18:18, 4 March 2010 (UTC)

Having a separate article on X-linked disorders perhaps makes sense, as the pattern of inheritance is rather different (and differs between sexes) and people sometimes get confused by that, so to explain this clearly in an encyclopedia one may need a separate article. As for autosomal dominant/recessive, I think that should be explained here in general terms, that is, applying to all organisms, not just humans. That is why I think an list of autosomal dominant disorders does not belong in this article: it distracts from explaining what dominance per se is and it is human-centered, whereas dominance occurs in every diploid organism (it was, of course, first discovered by Mendel in peas). Medical genetics belongs somewhere else. As for my reversion, please have a second look at what you did. It was wrongly formatted as a start, went against WP:MOS (the lead should start with "dominance is" or something like that, etc. One moment it spoke of "dominant alleles", in the next phrase it was "dominant traits". I am certainly not saying that the current article cannot be improved upon and I apologize if I discouraged you. I'm not sure what you mean by "journals semantics", though. As for merging ambidirectional dominance here, I'm not completely against that, but I am not sure that would not clog the article up in yet another way. As it stands, this article is (or should be) about phenomena at a single gene. (Ambi)directional dominance is something encountered in polygenic situations (and a concept used almost exclusively in quantitative genetics and it may be confusing to include it here. As for the article on "Autosomal recessive", did you actually click on that link? There is no article there, it is a redirect here... A final remark about the "confusing definitions" that you complain about: the current version of the article (although, I repeat, certainly not ideal) came about through heavy editing from an editor who has taught genetics for decades, so I gingerly suggest that the possibility exists that he knew what he was doing... --Crusio (talk) 21:22, 4 March 2010 (UTC)

Due to lack of time and sleep I came off rather disheveled and perhaps annoyed in my previous posts, including in my revision. For that I apologize. Please allow me to clarify: I do not disagree with the current definitions and discussions present within the article. There is disagreement in pinpointing an accurate definition of 'dominant', and I understand that you can talk about genetics without even needing the terms dominant or recessive because as I said in my edit "Classical concepts of genetic dominance and recessivity are simplifications of a quantitative reality". There are many exceptions where using the terms distracts from the real concepts. However, the central point of this article needs to be about defining and describing the ABSTRACT and PRACTICAL concept of dominance and recessive before going into the nuances of a genetically accurate definition.
That being said, I do not think Ambidirectional dominance needs to be merged with this article, I suggested that to make a point that you should be more open to having separate articles on the different topics of dominance (and to point out the fact that you referenced yourself 3/4 times in an article). That being said, In making my revision there were some formatting mistakes. I ran out of time to figure out the best way to format the numbered section and was hoping someone would help me fix it. I feel my definition was much more appropriate for introducing this article, it was taken from core up to date medical journals.

Here is what I believe needs to be fixed, and think my previous edit can be a starting point because it is a much improved introduction than the current near useless definition.
1) A better, more abstract and concrete definition of Dominance UPFRONT that can quickly be used for reference for someone in high school.
2) After establishing the abstract definition, a brief overview of flaws in the abstract definition.
3) Specific sections or different articles for Autosomal Dominant, Autosomal Recessive etc..
4) Somewhere, A list of human diseases, noting the uncertainty of such general categorization, that fall into the categories of Autosomal Dominant and Autosomal Recessive.
5) Citations, citations, citations, citations. The current citations are completely lacking.

I would have started doing this on my own, but now I feel that you might just revert anything you don't agree with rather than try to improve upon it. So, I encourage you to start these changes as you see fit and I will then work to improve upon them.UberMD (talk) 06:09, 5 March 2010 (UTC)

DOn't worry, we all have our off days and I know all about lack of sleep and being stressed :-) You should familiarize yourself with WP editing (for instance, your above comment uses extensive html code, which is discouraged for WP articles). Also, have a look at WP:MOS, so that your contributions adhere to WP's style guidelines. The reason I reverted you before was that I didn't readily see how I could improve on what you did, I do not do such things very often. I would advice to go slowly and incrementally. As for the points you mention:

Agree completely, the lead should provide a clear definition which it does not now.
Not sure, I'd like to see what you have in mind.
Autosomal dominant and autosomal recessive are flip sides of the same coin, so I certainly would not think that two different articles are justified. If you want an "autosomal dominant/recessive" article to concentrate on medical conditions, I would recommend a "list type" article, with an intro what it is about and then a list of disorders (with wikilinks).
See previous item.
The article currently indeed sorely lacks inline references.

As for relying on medical literature, I suggest that genetics literature is more appropriate as it will be more general (less human focused), more likely to be correct, and more likely to be up-to-date. For example, the classical article by Kacser and Burns (PMID 7297851) presented already in 1981many of the same ideas as the J. Pathol. article that you mentioned above. Genetics literature is also more likely to get nomenclature correct (such as the incorrect definition of co-dominance in J. Pathol. that I mentioned earlier). Concerning ambidirectional dominance, if you don't think it should be merged here, you should perhaps remove the merger tag. Also, if you feel that I gave to much emphasis to my own contributions, you are welcome to remove those references and replace them with more appropriate ones. Finally, you are relatively new here, so you cannot be aware of all WP policies and habits. Tagging an article to make a point about another editor's opinion is generally frowned upon (see WP:POINT). Don't get too upset if somebody disagrees with you or reverses your edits, assume good faith, they may have good reasons for their actions... :-) OK, back to real-life work, I have grants to review for an NIH study section next week... --Crusio (talk) 09:42, 5 March 2010 (UTC)

Not Good For A High Schooler

I'm Doing Some Research On Genetics, and my exams are coming up. I need each defintion for allele, gene, dominant, etc. This is NOT very helpful, I need more definition. —Preceding unsigned comment added by 194.126.24.54 (talk) 15:15, 16 March 2010 (UTC)

edit: read your textbook!!! —Preceding unsigned comment added by 128.91.66.134 (talk) 15:48, 17 March 2010 (UTC)

I agree. —Preceding unsigned comment added by 129.97.222.224 (talk) 22:59, 3 April 2010 (UTC)

For definitions, use a dictionary. For understanding, read and think. Smcewincarr (talk) 17:22, 27 December 2010 (UTC)

Recessive genes what?

I'm a computer programmer, thats my day job with a hobby in triva. I wanted to know what a "regressive gene" was, since apparently this is what gives people red hair. Unfortunatly even though "regressive gene" redirects to this article I am left utterly clueless by the article, even the summary is way way way over my head, in other words this article is inaccessible to the ordinary joe since it demands a level of specialised knowledge that the ordinary joe just doesn't have. Perhaps in the discussion of overhaul etc this can be take into account Jasonfward (talk) 14:04, 10 August 2010 (UTC)

I agree this article needs work, and have added {{confusing}} in the hope of attracting someone with the time and knowledge to work on it. For a quick and dirty answer to your question (leaving out plenty of caveats), I think you mean "recessive gene", which is a slightly sloppy way of saying "recessive allele". Humans generally have two copies of each gene, one inherited from each parent, and those copies may differ. A person will have red hair only if both copies correspond to red hair. A person who receives a copy corresponding to black hair from one parent, and a copy corresponding to red hair from the other parent, should have black hair. The allele corresponding to red hair is recessive to the allele corresponding to black hair. You could get a better answer at the Science reference desk. Adrian J. Hunter^{(talk•contribs)} 14:40, 10 August 2010 (UTC)

I would hope part of the purpose of Wikipedia is to avoid 'quick and dirty' answers that are inaccurate and mis-informative, even at the risk of making entries more complex. The caveats are critical. Here for example, 'recessive gene' is simply wrong: there is a 'gene locus' located at a particular physical position on a chromosome, we generally have two such chromosomes, and the specific forms of the gene on either chromosome are 'alleles'. Some textbooks might tell you that the 'black hair' allele is B, the 'red hair' allele is b, people with BB or Bb allele combinations have black hair, and only people with a bb combination have red hair. Thus one could say 'B is dominant to b' or 'b is recessive to B': B dominates b, which recedes. Bb parents can have bb offspring, but bb parents can't have Bb offspring. Simple. EXCEPT it's not accurate: it reflects the state of understanding 100 years ago. In fact, there are many genes that influence hair pigments, each has many alleles. You have red hair due to a pigment called phaeomelanin, black hair to eumelanin, and these are alternative modifications of dopaquinone. Production of melanin pigments is biochemically complex, see Wikipedia on 'Melanin', which is not flagged as 'confusing'.

It's late: a lawyer once presented a complex argument on a technical subject to a judge. Afterwards, the judge said, "After your argument, I am no wiser than before." The lawyer replied, "Yes milord, but you are much better informed." Smcewincarr (talk) 06:48, 27 December 2010 (UTC)

Oh. And when I was in grad school, there was a TV ad where a woman goes into the library and asks for a book on biology. The librarian asks, "I didn't know you were interested in biology." The woman replies, "Well, I wanted to know about ... constipation." — Preceding unsigned comment added by Smcewincarr (talk • contribs) 17:26, 27 December 2010 (UTC)

Recessive or dominance?

Wrong redirect from autosomal recessive to Dominance (genetics)? Meddoc13 (talk) 15:31, 23 August 2010 (UTC)

That's intended, as both concepts should be explained in the same article, and this is it. Ideally the lead should give an overview of both concepts. Adrian J. Hunter^{(talk•contribs)} 16:01, 23 August 2010 (UTC)

Dominance (incl. its variation such as "overdominance", partial dominance), recessive, and epistasis are gene actions (actually allele, but "gene action" is used very common). I would suggest this article retitled to it (gene action). Kembangraps (talk) 11:05, 25 August 2010 (UTC)

They're allele interactions or relationships. As far as I can see, "gene action" is used according to the ordinary English usage of "action" – a gene's "action" is what it does or where it does it [2][3][4]. Adrian J. Hunter^{(talk•contribs)} 11:50, 25 August 2010 (UTC)

Autosomal versus sex-linked dominance

This section gives the impression that the Y chromosome has no genes and will always leave the male with only one allele. Is this the case? It lacks an "Arm" and therefore lacks a lot of alleles, but surely not all of them?

I have added a reference to the Y-linked SRY gene. Males *always* have only one X allele, and one Y allele. The difference between an X and a Y chromosome is not that the Y 'lacks an arm' wrt X [X and Y are just names, not physical descriptions]. Detailed discussion of the Y chromosome is not really relevant to Dominance. Smcewincarr (talk) 16:23, 27 December 2010 (UTC)

The example about simple dominance seems to be wrong, and contradictory with the main article about eye color

This version about dominance genetics use as example the color of the eyes as a simple type of dominance: Dominance genetics
Text that I suppose to be wrong and contradictory with the other article:
A canonical example in a diploid species like humans is the simple 2-allele model of eye-color, where the brown (B) allele is dominant over the blue (b) allele.

The article about eye color: Eye color:
Text that I suppose to be right:
The once-held view that blue eye color is a simple recessive trait has been shown to be wrong. The genetics of eye color are so complex that almost any parent-child combination of eye colors can occur.[4][5]

Anyone knows a better and more accurate example? —Preceding unsigned comment added by 189.26.4.207 (talk) 13:29, 21 November 2010 (UTC)

The eye colour article is wrong: the refs do not support the statement (one ref does not say anything much, and the other is vague, and tertiary anyway). Blue/brown eye colour genetics is well established. The point being made is that eye colour is determined by other things as well – but this does not mean that the fundamental blue-brown mechanism is wrong. I've amended the eye colour article. Richard New Forest (talk) 20:17, 21 November 2010 (UTC)

Blue eyes are not a simple Mendelian trait, eye colour is polygenic, see review at [5] and OMIIM at [6]. In general, almost all of the 'classical' human genetic traits like arm-folding, hand-clasping, ear-lobes, tongue-rolling, and even PTC tasting are demonstrably not due to alternative alleles at single genes, and are thus not available as 'simple' examples without being inaccurate. To give accurate examples you pretty much have to go to medical conditions, like alkaptonuria, albinism, PKU, Cystic Fibrosis, retinoblastomca etc., in which case you have to provide a lot of background that complicates things more. Smcewincarr (talk) 05:54, 27 December 2010 (UTC)

Reverted edits by Smcewincarr

Hello All,

I just reverted several good faith edits by Smcewincarr. These contained at least one factual error - that gender is genetically determined, and made the intro much less clear, to my reading. I hope others will weigh in on those edits / my reversion. de Bivort 18:24, 27 December 2010 (UTC)

I've reverted the reversions. The sections up to homozygote / heterozygote were garbled, and included extraneous material. The Intro in particular used an incorrect example (eye colour) and missed the essential concept of Dominance. Physical gender *is* genetically determined, by an XY chromosome system in mammals; psycho-sexual gender is complex and not at issue. With respect to Dominance, the point is that in XY males there is only one copy of each gene on either chromosome (hemizygosity) and diploid rules do not apply. Smcewincarr (talk) 19:39, 27 December 2010 (UTC)

I reverted just the parts that I thought were worse in your version. The lede sentence in particular was much clearer before. It also accommodates instances of dominance that are not at the same locus, unlike your version. Also, really ... the proper term is "sex" not "gender" here. See, for example Sex-determination system. de Bivort 19:47, 27 December 2010 (UTC)

The lead sentence was not accurate; I have revised and simplified it further. Interactions between different loci involve epistasis, not dominance. Sex determination is OK.Smcewincarr (talk) 03:33, 28 December 2010 (UTC)

I would like to get other editors' opinions on the lede sentence. Dominance can certainly refer to different loci. The most conventional example I can think of is Dominant Negative mutants/transgenes, which act in trans at one or more loci. de Bivort 04:36, 5 January 2011 (UTC)

Dominant Negative mutants act on the other allele at a locus (thus acting in trans), not on other loci. Alleles have dominant/recessive relationships with other alleles at the same locus; they may affect expression of alleles at other loci, which is called epistasis. There are dominant and recessive forms of epistasis. Smcewincarr (talk) 17:02, 8 January 2011 (UTC)

If there are "dominant and recessive forms of epistasis" then the definition of Dominance should allow for dominant interactions between loci, which is, as you are saying the salient aspect of epistasis. de Bivort 18:59, 8 January 2011 (UTC)

No. The phenomenon is called 'dominant epistasis' because a dominant allele at one locus affects expression at another locus. The intergenic interaction is epistasis, not dominance. Smcewincarr (talk) 12:24, 13 January 2011 (UTC)

But this article is on "Dominance" as concerns the field of genetics. Surely "dominant epistasis" is an example of "dominance" in the field of genetics. de Bivort 17:40, 13 January 2011 (UTC)

Error in Epistasis

The last sentence in supplementary epistasis "This produces a characteristic ratio 9:7 ratio of unpigmented to pigmented plants" should be reversed to read "This produces a characteristic ratio 9:7 ratio of pigmented to unpigmented plants". The edit reflects the source already indicated. The difference is critical to understanding the ratio and gene expression phenomenon. — Preceding unsigned comment added by 66.90.172.138 (talk) 05:11, 21 September 2011 (UTC)

Fixed. You're absolutely right, and I've edited the article accordingly. Thanks for pointing that out. Please feel free to be bold and edit this article or any other in any way you see fit. Adrian J. Hunter^{(talk•contribs)} 05:43, 21 September 2011 (UTC)

on dominance

The article concerns Dominance. My intent in doing a major revision was to eliminate the previous articles conflation of 'dominant' with 'predominant', 'better', 'normal', 'higher enzyme level', 'adaptively superior,' etc., none of which have anything to do with the genetic concept. Dominant alleles and recessive alleles can be discussed in the same article, as can autosomal and X- or Y-linked dominant alleles. "Dominance" is a discussable concept, 'recessivity' is not. No introductory genetics text uses 'ambidirectional'.

The current lead gives a clear classical definition: Dominance is a relationships between alleles, a dominant allele is one that masks the phenotypic expression of a recessive allele. Mendel thought so, any introductory genetics text will tell you so, most using the word 'masks'. This requires reference to 'allele' and 'phenotype'

The inset pedigree is someone else's doing and contributes nothing towards the concept of dominance, as dominant and recessive alleles in the phenotypes are not specified. The tag about upper and lower case letters is out of place, and is already discussed in the text.

as to point 1) I have no idea what "more abstract and concrete definition" means

Veijia & Birchler (2009) citing a previous review state "Dominance is defined as a measure of the deviation of the heterozygote's observed trait value ... from its expected value based on the phenotypes of the two homozygotes. For instance, in a cross involving homozygous plants with red or white flowers, the resulting F1 flowers can be either red or white if the corresponding alleles are dominant, repectively [sic]." With due deference to Jim Birchler, the heterozygote has no 'expected value' apart from its *observed* phenotypic value in any particular cross between homozygotes. The second part obscurely states that the heterozygote looks like the dominant homozygote, which is not a definition but a characterization.

Subsequent discussion of the 'dominant' behavior of transcription factor mutants in disease is consistent with the current discussion of huntingtin protein, where the presence of the modified protein from a heterozygous genotypes makes an observable change to the phenotype.

as to point 2) "After establishing the abstract definition, a brief overview of flaws in the abstract definition", seems to suggest providing a flawed definition before offering a correct one. This is exactly the error done in most textbooks, where Mendel precedes Molecular and we go through the exercise of explaining wrinkled peas in the abstract before showing the consequences of defective starch branching protein for retention of turgor.

as to point 4) OMIM can be cited for a list of human diseases categorized as 'dominant' or 'recessive'; reference is included in the PKU example. It's irrelevant to discussion of 'dominance' as a concept.

As to 'citations citations citations': No modern genetics textbook discusses 'dominance' with inline citations. The concept requires simple explanation, not a historical review of successive approximations to the current understanding, or an abstract discussion like Veijia & Birchler. Anyone who wishes to write a scholarly discussion of the history of the concept of dominance with inline citations is welcome to do so, I would not waste my time doing so for Wikipedia, nor is this the purpose of Wikipedia.

Smcewincarr (talk) 04:09, 28 November 2011 (UTC)

Adding Regressive to Dominance

No they should not be joined. They are opposites. — Preceding unsigned comment added by 99.244.155.54 (talk) 15:20, 11 December 2011 (UTC)

I disagree. Recessive and dominant are opposites, but both are part of the theory of genetic dominance, which should deal with both. FilipeS (talk) 12:44, 6 February 2012 (UTC)

Codominance

As I understand, in codominance EVERY cell of the organism expresses both alleles and both contribute to phenotype. Then, why does the Rhododendron (photo) show some white parts and some red parts (in the same or in different petals)? It seems like a mosaicism rather than codominance. If every cell made the product of both alleles, every cell should be pink or red. I mean the two products should be present without combining in every cell, forming the same phenotype. The same for the blood groups AB0 in genotypes AB. They produce antigen A and antigen B in each and EVERY eritrocyte (there are not some eritrocytes with antigen A and some others with antigen B in the same individual). The example of blood types is clear, the example of the flower is not obvious. I can't understand the difference between codominance and semidominance in flowers as it is explained in the article. I can understand how they are different but not WHY (at molecular and cellular level). Is there a mistake here or am I missing something?--Miguelferig (talk) 22:04, 22 March 2013 (UTC)

All these terms (dominance, codominance, incomplete dominance) are based on the relationships between the phenotypes caused by different combinations of alleles. So the same pair of alleles can have have different relationships depending on which aspect of the cell or whole-organism phenotype is being considered. Because these terms are simplifications of the biological complexities of real cellular processes it's best not to interpret them too strictly. (Rosieredfield (talk) 16:35, 20 April 2013 (UTC))

Inaccuracies

There are profound errors on this page; in particular in 'Which trait is dominant?'. It absolutely IS traits that are dominant and recessive and NOT alleles; see http://www.ncbi.nlm.nih.gov/books/NBK7573/ Take sickle cell as an example: sickle cell disease is recessive; it only manifests in individuals who inherit two copies of HbS, so one might be tempted to say that HbS is recessive. But, sickle cell trait is dominant: it manifests in individuals who inherit one copy of HbS, so HbS is (apparently) both dominant and recessive. If you were then to look at the blood cells of a heterozygote (HbS/HbA) you would see some that sickle under low oxygen conditions and some that do not, which demonstrates co-dominance.

There are almost NO non-disease traits that display 'classical' dominant/recessive inheritance. One possible exception is wet/dry earwax (see the excellent Myths of Human Genetics). --Matstuff (talk) 09:53, 4 September 2013 (UTC)

Proposal to merge Recessive trait into Dominance (genetics) - again

Justification of proposed merge (based on WP:merging#Reasons for merger):

Context - "dominant x" and "recessive x" are exact opposites, inseparable from Dominance (genetics)#Complete dominance. To discuss one is necessarily to discuss the others.
Overlap (1/2) - The two articles are currently inconsistent. Please note that for the purpose of deciding whether to merge it does not matter which of the inconsistent alternatives is correct. The point is that merging the articles prevents any inconsistency and avoids contentious points being discussed in two places at once. eg:
- "dominant/recessive trait" vs "dominant/recessive allele" (which has been contentious in the Dominance article).
- "allosomal" vs "sex-linked" vs "X-linked".
Overlap (2/2) - "recessive trait" has some issues that could be simply resolved by merging:
- lack of references
- inclusion of a list of dominant/recessive traits
- The "See also" section of "recessive trait" has 3 distinct entries that all link to the dominance page (Dominance (genetics), Dominant gene, and Incomplete dominance).
- Introduction to genetics uses the Dominance page as its wikilink for "recessive". Due to the history below, there are probably similar cases elsewhere.
History - Equivalents of these pages were merged once in the distant past (May 2007, #Proposed merging and rename above), persisted in this state for many years, then split (in March 2011). As far as I can tell, the split occurred as a delayed side effect of the incidental breakage of the redirect of "Recessive" to "Dominance (genetics)#Recessive allele" during a major rewrite of the dominance article (28 July 2009). As such, I see no evidence that anyone ever made a deliberate decision to split. Shortly after the split there was a proposal to remerge that fizzled out with no meaningful discussion (split in March 2011, proposed remerge 26 Oct 2011, related discussion under #Adding Regressive to Dominance above, merge tags eventually removed as inactive 28 July 2012). The "recessive trait" article is therefore much newer than the "Dominance" one and appears to have received relatively little attention beyond reversion of vandalism and minor edits. In particular, the talk page is almost blank but includes a very tentative proposal to merge, which has received no response (it is an aside in the only talk page entry, which relates to a rename). The recessive trait article has <30 watchers whereas the Dominance article has >100.

Why am I not being bold? Mainly because despite its problems, the status quo has persisted for 2.5 years and the merge would be just short of a delete-by-redirect of the "recessive trait" article. The evidence I see suggests to me that the editors of the two articles have been largely unaware of the other article's existence, let alone its content but I can't quite beleive that is really the case. If this proposal receives as little response as the last one, my current intention is to attempt WP:BRD, maybe even before the full 30 days is up.

Nature of proposed merge:

The most important aspect would be to make absolutely clear that "recessive" is part of the subject of this article. This must apply both to those who arrive at the merged page from a "recessive x" redirect (who will otherwise be likely to recreate a "recessive x" page) and future editors of the Dominance article (some of whom will be likely to remove or reduce references to "recessive"). I propose as strategy that the first sentence of the lead must contain "dominant and recessive", bolded to make clear that these terms are part of the subject of this article, not just related concepts. As a concrete example (purely to illustrate the strategy), I propose "Dominance in genetics is a relationship between two alleles of a single gene, in which one allele is dominant, masking the phenotypic expression of the second allele, which is recessive."
The other important aspect is what parts of the existing articles to keep. I see the merge as being just short of a delete-by-redirect of the "recessive trait" article, in which case the question is "What bits of that article are worth saving?". I don't mean to imply that the existing article is awful, only that I'm finding it hard to identify any aspects that are either significantly better than in the Dominance article, or unique to the recessive traits article and desirable for inclusion in the Dominance article. My initial thoughts are:
- Preserve something about estimating carrier frequency for a recessive trait based on the frequency of the dominant and recessive phenotypes.
- Find a place for the autorecessive image.
- Maybe reuse the pea plant text as IMO the existing Dominance article is overly abstract (ie in need of an "Examples" section) and the recessive trait#Pea_plant text is already formatted as an example (whereas the one in Dominance#History isn't).
- Add Punnet square to "See also" (but don't keep any of the related recessive trait text).

End of initial proposal. TuxLibNit (talk) 00:25, 28 December 2013 (UTC)

Go for it! Rosieredfield (talk) 02:32, 28 December 2013 (UTC)

Support without reservation, and no need to wait 30 days. Two sides of the same coin. Adrian J. Hunter^{(talk•contribs)} 10:13, 28 December 2013 (UTC)

Support. Difficult to explain one without the other. Context can be provided for both in the same setting. JFW | T@lk 21:40, 28 December 2013 (UTC)

Support Really makes sense. Lova Falk talk 14:51, 20 January 2014 (UTC)

I've merged the few bits I thought needed doing. Main change was on 6 Jan and redirects were 18 and 20 Jan. TuxLibNit (talk) 23:45, 20 January 2014 (UTC)

Proposal to merge Codominance into Dominance (genetics)

I plan to start by boldly merging, so this section is intended to serve as a justification for that action and a starting point for discussion if it gets reverted.