From Wikipedia, the free encyclopedia
Jump to: navigation, search


What is the origin of the word 'ploidy'? A lack of familiarity with the root of this word is what makes it confusing to readers. —Preceding unsigned comment added by (talk) 09:42, 25 August 2009 (UTC)

Old comment[edit]

There is little more than a dicdef here; I propose moving the Haploidy, Diploidy, Haploidisation, Polyploidy, and Aneuploidy pages to Ploidy. You have to read all those articles to understand ploidy anywho. I'll be happy to do the merge after approval. Lefty 16:03, 2005 Mar 12 (UTC)

also Haplodiploidy. Lefty 16:08, 2005 Mar 12 (UTC)
Let's add Merodiploid while we're at it.Dr d12 (talk) 23:17, 27 February 2009 (UTC)

"Number of homologous sets of chromosomes"?[edit]

This is a confusing definition. One might read this to mean "homologous sets" (ie: sets of homologous chromosomes), or homologous "sets of (non-homologous) chromosomes." For example, the number of homologous sets of chromosomes in humans is 23 if one considers a "set" to be one pair of homologous chromosomes, or it could be 2 if one considers a "set" to be the collective number of non-homologous chromosomes.

Ploidy therefore refers to the number of sets of non-homologous chromosomes, not homologous chromosomes. Perhaps a more accurate definition would be something like, "Number of homologous sets of non-homologous chromosomes." 20:39, 3 August 2007 (UTC)

Agree with the above. The set of chromosomes must be well-defined. I propose a primitive but clearer definition of "ploidy" as "the number of (homologously) repetitive sets of all the non-homologous chromosomes in a biological cell". —Preceding unsigned comment added by (talk) 04:41, 9 October 2007 (UTC)

looking away from diplontic organisms..[edit]

Euploidy/aneuploidy can also be defined in terms of genomes (e.g. Kondrashov, AS. 1997. Evolutionary genetics of life cycles. Annu. Rev. Ecol. Syst. 28: 391-435) such that euploidy means having one or more complete copies of a genome. By this definition, eukaryote cells (which carry part of their genome in mitochondria and plastids as well as the nucleus) are frequently aneuploid, as there may be multiple copies of plastids/mitochondria present for each nuclear copy.

Halfsnail 13:55, 31 May 2005 (UTC)
  • I'm not sure that this definition is standard. If it was all eucaryotes would be aneuploid. Another issue is that as genomes are sequenced it is becoming obvious that organisms that were considered diploid are actually ancestral tetraploids. Where the line is drawn between tetraploid and diploid will thus be quite controversial for some species. David D. 15:55, 31 May 2005 (UTC)

The term "aneuploidy" refers to an abnormal numbers of nuclear chromosomes; extra-nuclear genomes are not counted. It's commonly used in the description of immortalised cells (cultured cell lines or cancerous cells) where crazy chromosomal events go on, with cells replicating DNA but not dividing or randomly degrading chromosomes. Aso, for describing monosomy or trisomy conditions such as Down's. The issue of ploidy for an organism will be decided (I predict!) based on active copies of genes. Humans generally have two active copies of autosomal genes (ignore X chromosome genes and other special cases for the moment), and are therefore diploid. Xenopus laevis, being "pseudotetraploid" has four copies of each gene but in two pairs of identical copies. So functionally, it has two active copies of each gene, hence the "pseudo-" prefix. Doctoremma (should I leave an email?)

Are we sure "haploid" comes from Greek for "simple"? For years I've been under the impression that it meant "half ply" -- that there was initial confusion as to what would be considered the "normal" complement of chromosomes, and haploids were so called because they had half the number that diploids did. -—Preceding unsigned comment added by (talkcontribs) email address removed -postglock 06:59, 31 August 2006 (UTC)

"Haplo" means "single" or "one". Doctoremma again.

Haplodiploidy... what about Haplo-diploid sex-determination system?[edit]

Merge? I would prefer that Haplodiploidy is merged into Haplo-diploid sex-determination system, because it would then match the other articles on sex-determination system. Kirbytime 23:48, 12 April 2006 (UTC)


I'm pretty sure this section is wrong, according to my uni lecture notes and biology dictionary. I would just like someone else with a little more knowledge to write this correctly. As far as I can determine, euploidy is having integral multiples of the haploid number of chromosomes, i.e. haploid, diploid, triploid, tetraploid, etc. This seems to suggest to me that the euploid number (if there is such a thing) would be equal to the haploid number...? But i don't really want to put this in unless I am sure. -postglock 12:20, 30 July 2006 (UTC)

I wouldn't use the term "euploid number" - it doesn't mean anything. You're right, an organism is "euploid" if they have normal integer multiple of the haploid number. If this is 1x or 2x, they are simply called "euploid" (because these are the norm for most animals). If they are 3x or more they are "euploid" and more specifically "polyploid". Doctoremma.

I think that Postglock and the article (edited by Postglock??) are using the word integral incorrectly. I believe that the proper word (based on context) is "integer." This is incorrect in the article.

Ploidy vs monoploid number?[edit]

I did not understand from the article what ploidy is or what monoploid number is. For this reason, I did not understand most of the article. What is the difference between ploidy and monoploid number? The two introductory sentences suggest that one is a concept that indicates the other, but this needs to be made clear. The first sentence must be written to say what ploidy is. -Pgan002 05:33, 10 September 2006 (UTC)

As far as I am aware, ploidy is the number of sets of chromosomes, e.g. in humans diploidy = 2 sets of (non-homologous) chromosomes. Tetraploid organisms have 4 sets, etc. The monoploid number (N) is the number of chromosomes within a monoploid (single non-homologous) set, i.e. in human, N=23. I think you might have made an error in your edits referring to this, I'll check again later if I have time... -postglock 07:32, 10 September 2006 (UTC)
Thanks. I corrected the definition of monoploid number in the article.
Unfortunately, that definition is not consistent. For example, Emmer wheat has the AABB chromosome sets (28 total chromosomes) from Triticum monococcum (AA, 14 chromosomes) and T. searsii (BB, 14 chromosomes). It is an amphidiploid, and the A's and B's are different chromosomes. Even more dramatic is rutabaga (Brassica napus), which has 38 chromosomes and is tetraploid. It is also an amphidiploid, with one set having 20 chromosomes (from B. campestris) and the other having 18 chromosomes (from B. oleracea). TedTalk/Contributions 17:54, 20 September 2006 (UTC)
I do not understand what this means, because it does not use the terms in the definition, and I do not know enough biology. As I understand, the definition says that the set of all chromosomes in a cell is partitioned into subsets, and however the subsets are defined, they all have the same number of elements, and that number is called the monoploid number of the cell. I think you are saying that Emmer wheat has 28 chromosomes, 14 of which are not homologous with the other 14. What's the problem? And what is the monoploid number of Emmer wheat? -Pgan002 22:19, 20 September 2006 (UTC)
Monoploid Emmer wheat is not defined -- it never exists. The gamete is AB -- which is diploid, having 14 chromosomes. For Rutabaga, the total number of chromosomes is 38 and is a tetraploid. The number in the gametes is 19, which is diploid. However, you can't evenly divide 19 chromosomes in half. If I separate them into the original species, then they are monoploid, but not rutabagas (they would be haploids for the original cabbage and turnip). There is no monoploid variety. On the other hand, we can find monoploid, diploid, triploid, and tetraploid tobacco.
I can give a definition, which I use in my class, but it would probably be considered original research. I'll see if I can find a real citation for it. TedTalk/Contributions 02:12, 21 September 2006 (UTC)

Homologous set[edit]

What defines a non-homologous "set" of chromosomes? As I understand, homology is a matter of evolution, and so is hypothesized, not an observable variable. Therefore looking at two chromosomes, the best we can say is that we believe they are (or are not) homologous. And so the ploidy of an organism is (by definition) also hypothesized rather than being directly observed. This is far from clear in the article. -Pgan002 21:05, 17 September 2006 (UTC) (edited 2006-09-19)

Evolution has nothing to do with describing chromosomes as homologous. During Prophase I in meiosis, the synaptonemal complex pulls together homologous chromosomes. This term pre-dates the current use of the word homology. The complication arises when looking at amphidiploids, since they will pair up under their "old" chromosomes. At that time, sequence similarity is used to determine the original chromosomal sets. TedTalk/Contributions 12:56, 18 September 2006 (UTC)
Thanks! That clarifies it a lot. I updated the article, and added explanations from your comments to homologous chromosome and homology (biology) -- please review them for correctness. Some things are still unclear:
  1. Does each chromosome in a given cell have the same number of homologues? Can it be said that ploidy is the number of homologoues of chromosomes that have homologues (plus the chromosome itself)? What if there was a cell where some chromosomes have one homologue each, while others have two?
  2. What about the X chromosome and Y chromosome in male humans? By the definition they do not belong to any homologous set, since there is no non-identical chromosome that represents the same biological features. But applying this reasoning to monoploid organisms, it turns out that they have a ploidy of zero, since none of their chromosomes have any homologues.
  3. It follows from the definition that male humans have a monoploid number of 22, while females have 23 (including one X-X pair). Is that right? -Pgan002 07:34, 20 September 2006 (UTC)
The treatment of homologous chromosomes and ploidy in Wikipedia is pretty bad. One problem is that there isn't a nice clean definition -- all of them have faults and run into problems. My usual first step in definitions is to pull out Robert C King and William D Stansfield (1997). A Dictionary of Genetics. Oxford.  They define homologous chromosomes as: "chromosomes that pair during meiosis", which is the classical cytological definition. This means that X and Y are homologous. However, it runs into problems with amphidiploids, and the number of homologs it would give is x (number of chromosomes in gametes), not n. Unfortunately, King and Stansfield go further and give the molecular geneticist definition as well: "homologous chromosomes contain the same linear sequence of genes and as a consequence each gene is present in duplicate." This definition is in parallel with sequence homology. This would exclude nearly all of the X as homologous with Y (all but the pseudo-autosomal region) -- but we don't normally talk about partially homologous (unless we are talking about translocations...a whole other can of worms). For your questions:
  1. If you use the cytological defintion, then yes, outside of somatic aneuploid mutations and the gametes. If you use the linear sequence homology defintion, then no.
  2. The cytological defintion states that X and Y are homologous. The sequence homology definition breaks down and comes up with some very unsatisfying answers. Monoploids are no problem with either defintion: since all chromosomes are distinct, there is one set.
  3. The cytological definition gives human males and females n as 23. Good luck trying to make sense out of the sequence homology defintion.
Homologous chromosomes are really a cytological feature -- most molecular geneticist I know of looking at homology don't really concern themselves with homologous chromosomes. As such, it is better to use the cytological definition. Deciding on a good definition for ploidy is another question entirely, and neither camp is very good at it! TedTalk/Contributions 14:38, 20 September 2006 (UTC)
If you want to find a consistent definition of homolgous chromsomes and ploidy number, then you have to find a defintion that works seamlessly with X and Y on the one hand and amphidiploids on the other hand, and with inversions on the third hand. I know of no good definition that works with all those situations. TedTalk/Contributions 14:46, 20 September 2006 (UTC)
I tried to reflect these ideas in the articles, but you are certainly better qualified to do this. Would you mind reviewing it? -Pgan002 21:04, 20 September 2006 (UTC)
Why is it a problem to accept that chromosomes of ampydiploids have x homologs? What is the intuition that it should be n. -Pgan002 21:57, 20 September 2006 (UTC)
Sounds like ploidy is a flawed conept to start with. I am often amazed at how heavily such concepts are used in science. Biology seems to be particularly wraught with them. -Pgan002 21:04, 20 September 2006 (UTC)
No, it really isn't flawed. It is just hard to define, particularly as the terminology from classical genetics is reused in a different manner in molecular genetics. It is one of those cases where things become harder when you try to include all the exceptions and strange situations. That is biology. TedTalk/Contributions 02:17, 21 September 2006 (UTC)


What is a haploid cell? The article only defines haploid number. Is this a good definition: "A haploid cell is one that contains half the number of sets of chromosomes that other cells of the organism contain."? -Pgan002 23:39, 27 September 2006 (UTC)

Haploid and monoploidy contradiction[edit]

The section says "The gametes of common wheat are considered as haploid since they contain half the genetic information of somatic cells, but are not monoploid as they still contain three complete sets of chromosome from three species of organisms"

I'd therefore expect to see "x = 3n", but it says instead "n = 3x".

Am I missing something? —The preceding unsigned comment was added by Sagie (talkcontribs) .

You are right. I've edited the article to follow. Thanks. -postglock 23:03, 14 November 2006 (UTC)

...and I've edited it again, since haploid is mistaknely used where monoploid should have been in one section. Marchino61 (talk) 07:04, 14 January 2014 (UTC)

Males and Females in Haplodiploid Species[edit]

The article states:

A haplodiploid species.... Most commonly, the male is haploid and the female is diploid. ...
... One consequence of haplodiploidy is that the relatedness of sisters to each other is higher than in diploids....

This is a bit confused, since it has switched from dealing with haploid males and diploid females, to diploid males and haploid females, with no overt notice to the reader. Admittedly, the prior paragraph only says, "Most commonly," and I can follow it as I am familiar with the topic from reading Richard Dawkins' The Selfish Gene, but I think a reader trying to understand this for the first time might be thrown for a loop. — DavidConrad 04:19, 23 November 2006 (UTC)


Should the article mixoploidy (currently just a stub) be merged here? --David Edgar 11:08, 20 February 2007 (UTC)

I think so. Pgan002 21:54, 14 June 2007 (UTC)
OK, I did it. --David Edgar 10:18, 15 June 2007 (UTC)

this section needs citations--Vitki1963 (talk) 15:59, 30 August 2013 (UTC)

Monoploid v Haploid[edit]

The article says "Male bees, wasps and ants are also monoploid. For organisms that only ever have one set of chromosomes, the term monoploid is sometimes used interchangeably with haploid, but this is no longer the preferred terminology." When I talk about hymenopteran reproductions, I always say "haploid male". Should I be saying "monoploid male" instead? But the article title is Haplodiploid sex-determination system; should the word "haplodiploid" become "monoplodiploid"? Web searching on "monoplodiploid" gets precisely zero hits. I think this supposed deprecation of "haploid" (to refer to a mature individual as opposed to gamete) is overstated. Fungi are monoploid, but male bees are haploid. —  Randall Bart   Talk  19:14, 31 August 2007 (UTC)

Confusing from the first par[edit]

It's pretty revealing when you have to go to the Talk Page to try to nut out what is being said in the article, and find there rather clearer definitions and explanations than in the article itself. Posters have been complaining about this "ploidy" stuff for years, but it looks just as bad now as it did then. Take the first par.

Ploidy is the number of homologous sets of chromosomes in a biological cell. The ploidy of cells can vary within an organism. In humans, most cells are diploid (containing one set of chromosomes from each parent), but sex cells (sperm and egg) are haploid. In contrast, tetraploidy (four sets of chromosomes) is a type of polyploidy and is common in plants, and not uncommon in amphibians, reptiles, and various species of insects.

First, the term “haploid” is utilized but not defined, which is a big no no. When it is mentioned again, it is within a rather confusing context of monoploidy and haploidy.

Second, raising the subject of the sex cells as compared to the somatic cells at this very early stage is unnecessary and likely to futher confuse the reader. This topic should be broachcd later.

Third, all the definitions are thrown in holus bolus, without much logic as to how they are arranged. It appears that when all the different varieties of “ploidy” were amalgamated here, not enough effort was made to integrated them seamlessly. And often, technical terms are used without the author defining or explaining them. Further, some are just ambiguous. For example, what is a “unique chromosome” ?

I’m not proficient in this field otherwise I’d have a go. But at the moment, the whole article is murky and badly organised. Could someone have a bash at this? Myles325a (talk) 22:52, 26 December 2008 (UTC)

Your points are good ones, but I don't see any way to leave out sex cells in the intro, since the definitions of diploid and haploid rest on the chromosome numbers of zygotes and gametes respectively. How could we make this clearer?--Curtis Clark (talk) 02:58, 27 December 2008 (UTC)

I think I have to agree with Myles325a. My daughter was studying for a biology test (a subject that I never took), and was reading aloud about how spores are haploid. I found this confusing, thinking that this meant that two spores needed to meet up before an organism could grow. So I looked it up in Wikipedia, but I felt not much wiser now than when I started. (I *think* I understand if now -- organisms that grow from spores don't NEED two pairs of chromosomes, right?) Would it be possible to write something so that a relatively intelligent person who is completely ignorant about the subject could get an introduction to what it is about (which is kind of the purpose of an encyclopedia). But please don't answer my questions here in the talk page; rather, improve the article so the reader wouldn't need to go to the talk page.Ifdef (talk) 14:19, 7 December 2009 (UTC)

1 or 2 different?[edit]

"The exact number of chromosomes may be one or two different from the 2 number yet the cell may still be classified as diploid (although with aneuploidy)."

Is it just me, or is this sentence really unclear about what it's talking about? I would edit it to make it more understandable, but I'm not even sure what it's trying to say. Hopefully someone else can get in there and fix it. (talk) 17:42, 14 January 2009 (UTC)

Yes, I think it is better without that sentence, and have removed it. To call such organisms diploid is common, but rather careless terminology. "Diploid or near diploid" would be preferable. The explanation of aneuploidy higher up the page seems to be sufficient. Nadiatalent (talk) 12:44, 31 October 2010 (UTC)

Germ cell versus sex cell[edit]

Recent edits involved changing germ cell to sex cell and back again, when the meaning was post-meiotic cells. The wording was perfect as germ cells, e.g. but the idea of distinguishing gametes from their precursors, and calling the precursors germ cells, seems to be overwhelming basic education, see for example: I've changed it back to sex cells, because students might have been trained to think that "germ cells" was wrong. Guess we'll have to work on explaining this all even more clearly. Nadiatalent (talk) 12:31, 31 October 2010 (UTC)

Inappropriate lead[edit]

In addition to all the problems noted above, the leading section of this article is not a summary, as it should be, but includes key material for understanding the article as a whole which is not repeated elsewhere. Peter coxhead (talk) 17:38, 18 December 2011 (UTC)

"Diploid" inconsistency[edit]

The article uses diploid in two ways: 1. To refer to cells carrying twice the haploid number of chromosomes (as in Strasburger's original usage) 2. To refer to cells carrying twice the monoploid number, so having two homologous copies of each chromosome, ignoring difficulties about sex chromosomes (as commonly used now)

The distinction becomes important when dealing with polyploid species - say the hexaploid wheat example commonly used, which has haploid gametes but is otherwise hexaploid. According to sense 1, however, the plant would be simultaneously diploid and hexaploid (with haploid/triploid gametes). This is confusing, and as far as I know, "diploid" is never used in such a case. An instance of this from the article: "All plants and many fungi and algae switch between a haploid and a diploid state (which may be polyploid)"

I'd like to either switch all to one usage (probably sense 2), or add an explanation that diploid is used in two quite different ways (if it ever is outside this article). I just can't find a way to rephrase my sample sentence above to sense 2! Here's one effort:

"All plants and many fungi and algae switch between a haploid and a higher-ploidy state"

Also note that even using sense 1, the original sentence would be more correct this way: "All plants and many fungi and algae switch between a haploid and a diploid state (both of which may be polyploid)" Grothmag (talk) 20:06, 22 August 2012 (UTC)

Yes, this problem is one of long standing in genetics, and is undoubtedly due to the fact that humans tend to think that diploidy is all that matters. The term "monoploid" helps with some cases, but I agree that your last suggestion is an improvement. I suspect though, that someone will then come in and claim that diploids can't be polyploid, or something. Sminthopsis84 (talk) 16:34, 23 August 2012 (UTC)
"I suspect though, that someone will then come in and claim that diploids can't be polyploid" Actually, I'll go ahead and make that claim, or rather, ask for a citation to the contrary, for the article. I've searched for one, but all sources I've found, which naturally talk of haploid & diploid phases, do not explicitly use "diploid" to refer to a phase that is anything other than 2x. Most work under the usual assumption of monoploid gametes and diploid zygotes, and where polyploidy is mentioned, skirt around actually talking of haploid/diploid phases at all. This includes Strasburg's original text. As far as I can determine, diploid is always used to refer to the 2x state, though I'd be happy to see (and add to the article) a citation to the contrary! Grothmag (talk) 20:55, 30 August 2012 (UTC)
It is certainly rather scrambled (partly my fault). Rieger, R.; Michaelis, A.; Green, M.M. (1968). A glossary of genetics and cytogenetics: Classical and molecular. New York: Springer-Verlag.  would seem to be the citation to use. "Functional diploid" and "segmental allopolyploid" concepts might need to be introduced. Sminthopsis84 (talk) 22:55, 30 August 2012 (UTC)
It's not so bad, but there are two definitions of diploid used, and I think that should be clarified. A pity this isn't the place to define new terms, since clearly a disambiguation term would be helpful - akin to the haploid/monoploid distinction, perhaps something like duploid/diploid would be better for everyone (since a term for 2x is useful, but so too is a general term for the 2n state). Does Rieger et al. actually support the use of haploid/diploid for organisms other than the "usual" x/2x haploid/diploids? They define haploid as "of cells or individuals with a single genome or chromosome set...", which excludes higher ploidies.
I note that Rieger et al.'s glossary actually includes the term "dihaploid", to denote the "haploid" state of a tetraploid. So rather than using haploid/diploid for all, one would use dihaploid/tetraploid (and presumably trihaploid/hexaploid ...), as appropriate. Perhaps it's better to talk of "haplophase complement" and "diplophase complement", and reserve diploid for the 2x case only? Grothmag (talk) 18:46, 31 August 2012 (UTC)
This is a specific example of a issue which comes up quite often in biological terminology – actual usage by biologists is demonstrably confused, but in Wikipedia we can only go so far in Clarifying it without falling foul of OR. It is sometimes rather frustrating! Peter coxhead (talk) 20:28, 31 August 2012 (UTC)
I believe that the confusion comes from some people talking about newly created polyploids that might not be fertile, so they want to talk about 4n, while others talk about "functionally diploid" established polyploid species such as hexaploid wheat, so they want to say 2n=6x. The latter is a particularly useful terminology for triploids, 2n=3x, which encapsulates what happens during meiosis in a triploid: two sets of chromosomes pair and segregate, and the third set distributes randomly, producing gametes with a range of chromosome numbers; just like arithmetic, on average the gametes are 1.5x. Sminthopsis84 (talk) 22:32, 31 August 2012 (UTC)
I agree with Peter that the terms have been confusing in biology for a long time (I was initially confused in the 1970s, and went on to figure it out and study polyploid plants). I'll add that attempts to regularize and de-confuse biological terminology have met with limited success: it's hard to find newer sources that call angiosperm ovaries "ovularies", although the alternate term would save much confusion about the basic nature of the plant life cycle.
The 2n=6x terminology is the norm when people who study polyploidy communicate with each other (at least in the US), and it's fairly common in the literature. It completely skirts the issue raised here, and I think that's why it is so prevalent.--Curtis Clark (talk) 23:08, 31 August 2012 (UTC)
Very confusing indeed, since I now realize that the "haploid" definition is also incorrect, or at least incomplete. PK Gupta's "Cytogenetics" has a good overview of the terminology in plants; I hadn't encountered the 2n = x sense of haploidy before (though this is still referring to the gametic number of chromosomes, so that part's consistent with the article). However, I'm now convinced that the tinkering I was planning would make the article less readable and less useful, and probably no more accurate. So, I'll leave well enough alone. Interesting discussion, though! Grothmag (talk) 23:30, 5 September 2012 (UTC)
About your most recent edit however, Sminthopsis84, you now have this: "...the monoploid number (x), which is the number of unique chromosomes in a single complete set in polyploid organisms...". Wouldn't it be more accurate without these last three words? Isn't it just as correct to use x, or the monoploid number, when discussing diploid organisms? Grothmag (talk) 23:35, 5 September 2012 (UTC)
I agree.--Curtis Clark (talk) 03:16, 6 September 2012 (UTC)
Indeed, I've removed that mis-step. Not sure that the text is very readable even without it, ... This is very close to a hilarious situation, in my opinion, we all know a lot but still can't get this explained sufficiently well! Sminthopsis84 (talk) 15:48, 6 September 2012 (UTC)

Offspring of diploid + tetraploid parents[edit]

Could you explain the process (meiosis?) of reproduction from parents, 1 with diploid cells, the other with tetraploid cells?

In Oysters, it can lead to triploid new born oysters.

How is that? As gametes should be haploid (= monoploid) !!!

The process of mixing diploids & tetraploids is a man made selection of sterile commercial shells. What is the nature of the advantage of triploids? Is this the sterility that preserves energy for faster growth? I read tetraploid oysters are highly dangerous to the species, as in case of escaping out of laboratories, it could interact with wild oysters and generate sterile populations.

What about other species? Could this happen elsewhere?

What is the connection with hybridization, such as for corn? — Preceding unsigned comment added by (talk) 16:35, 23 August 2013 (UTC)

Fertilisation is the process involved. The diploid produces monoploid gametes (1x), and the tetraploid produces diploid gametes (2x). When these get together the result is triploid (3x) offspring. They are sterile because they can't neatly divide their chromosomes during meiosis. What happens in Taraxacum officinale pollen meiosis is that two sets of chromosomes evenly divide, but the third set gets scattered, so that overall, the gametes have all sorts of chromosome numbers, most about 1.5x. The gametes with strange chromosome numbers (not 1x or 2x) cannot make an offspring that develops normally because the genes on the chromosomes aren't properly balanced. In Taraxacum officinale it doesn't even get to that stage, the pollen grains don't develop properly and die. Yes, if tetraploid oysters were released from a laboratory, their sperm and eggs would combine with sperm and eggs from the wild oysters, but those offspring would be sterile triploids. Yes, something similar could happen in other species, and it also happens in nature when a spontaneous tetraploid is formed. For the corn question you might want to look at Open pollination. Sminthopsis84 (talk) 14:06, 24 August 2013 (UTC)


The connection between "haploid" in the sense "one set of chromosomes present" and the use of the word in "haploid number" is not clear in the article. The article introduces the term "haploid number" before even defining "haploid", and the section "Haploid and monoploid" seems to think that it should start by defining "haploid number" even though it then goes on to use the word "haploid" in (as far as I can see) another sense.

Furthermore, haploid redirects to the section "Haploid and monoploid", but that section does not actually define what "haploid" means in any helpful way. Instead, it uses the term as if readers should already know. This is not very useful when clicking on links in other articles (e.g. "Each pollen grain is a male haploid plant" at Pollination, or "It produces gametes and is typically haploid" at Gametophyte). Reading the linked section does not shed any light on what a "haploid plant" might be, for instance.

I think someone familiar with the subject and article organisation should look at this. I don't feel confident about fiddling with it since I know nothing about the subject. (talk) 20:34, 18 September 2013 (UTC)

I think there's general agreement that the article is confused/confusing. There is a definition of "haploid" hidden in the lead section, which doesn't do what it's supposed to, i.e. summarize the article. However, no-one has yet come by with the expertise and time to sort this out. Peter coxhead (talk) 21:31, 18 September 2013 (UTC)
Ok, I've attempted to rewrite the section Ploidy#Haploid and monoploid so that it's clearer. I would be grateful for any comments on whether I've succeeded! Peter coxhead (talk) 09:04, 19 September 2013 (UTC)
Great work. As far as my original gripe is concerned it is much much better now. (talk) 19:21, 19 September 2013 (UTC)
I'd like to try to rewrite more of the article, but then I run into the problem discussed in at least one thread above: sources are inconsistent and it's hard to write an account which maintains a neutral position but remains readable. Peter coxhead (talk) 21:27, 19 September 2013 (UTC)

Source needed that says terminology is confused[edit]

As is clear from the discussion above, the core problem is that sources use terms in a confused way. I think the article would be clearer if we were able to explicitly say this without committing the sin of OR. Does anyone know of a source which says that the terminology is confused? Peter coxhead (talk) 21:42, 19 September 2013 (UTC)

To be really precise, the confusion which interests me can be illustrated by any even-numbered ploidy, say a tetraploid.
  1. A tetraploid can be described and defined in terms of the monoploid number x via the formula 2n = 4x, which says that the "diploid phase" (the 2n phase, the zygote or sporophyte) has four sets of chromosomes with x in each set – the ploidy is the multiple of x. The "haploid phase" (the 1n phase, the gamete or gametophyte) has two sets of chromosomes. In this approach, for ploidies higher than 2, n and x have different values; it's the multiple of x which primarily defines the ploidy. A tetraploid zygote or sporophyte is tetraploid with respect to x but diploid with respect to n.
  2. Alternatively, a tetraploid can be described and defined via the formula 4n, without referring to or mentioning in any way the monoploid number x. The zygote or sporophyte is described as tetraploid (4n), the gamete or gametophyte is described as diploid (2n). In this approach, there is no x; it's the multiple of n which defines the ploidy.
I can find both uses in the literature, but (as yet) no source discussing them both. Peter coxhead (talk) 09:50, 20 September 2013 (UTC)
A comment about why this problem occurs: in natural conditions, with organisms that carry on growth and sexual reproduction successfully, the ploidy level is more-or-less irrelevant in the sense that meiosis divides everything by two and fertilization doubles it again, 2n -> n and back again. One might wish to make the point that one had created in a petri dish a very unstable organism, and so would want to say 4n rather than 4x. There are heavy and serious textbooks and dictionaries of genetics that are very definite about what terminology they consider acceptable. A problem we have here in wikipedia is that these authoritative textbooks are rather old, but there is a lot of half-baked class-notes-sort-of-material online that wikipedians are tempted to think is more up-to-date and therefore better. For established species that reproduce sexually, I would emphasize that it is a major mistake to talk about a tetraploid as 4n; that would imply that it is incapable of meiosis, can't align its chromosomes as two sets. In much early literature about hybrids that reproduce by apomixis and about induced polyploidization (such as with colchicine applied to plants) these sorts of phenomena were important, but research emphasis has moved away from the mechanics of meiosis at that level. We could discuss particular documents, but in my experience misuse of the 4n terminology is quite common and quite sad. Sminthopsis84 (talk) 22:13, 22 September 2013 (UTC)
I entirely agree that the 2n = Px terminology is better. But it's not just online notes that use the Pn definition, but some respectable textbooks and glossaries. Sigh... Peter coxhead (talk) 20:23, 23 September 2013 (UTC)

I have an email from one of my genetics professors, saying that standard textbooks use n where they actually should use x (e.g. wheat is 2n and 6x but some books state that it is 6n). If we cite this, is that sufficient to avoid being accused of "original research"? I'll happily provide this email and get his permission if it could be of use.

Marchino61 (talk) 07:09, 14 January 2014 (UTC)

Unfortunately, an e-mail isn't a reliable source according to WP:RS. Now if he's written this in a paper or textbook, that would be another matter. Peter coxhead (talk) 16:06, 15 January 2014 (UTC)
I don't know of a source either, only the reliable literature that those of us who care about the matter use, which defines only the more rigorous n and x terminology because both concepts are used. A source that discusses both would have to be a transient document, similar to marginal notations on a student's essay, which is not likely to be published in an RS. Sminthopsis84 (talk) 16:50, 15 January 2014 (UTC)
If you stick to formulae, using only numbers + n or x, then there need be no confusion (although there often is). However, as soon as you use words instead, there's a problem. 1x is monoploid whereas 1n is haploid; two formulae, two words. But what are 2x and 2n? They are both diploids. There just aren't two words. So you have to decide from the context whether "diploid" means 2x or 2n. Just as one example, look at these lecture notes. If you search for the word "diploid", the first occurrence defines it as 2x but the next occurrence says that genome composition AABB, i.e. 2n = 4x, is a "functional diploid". This isn't a confusion on the part of lecturer; I think the notes are very clear. It's the result of an inadequate terminology, but we can't invent one, and unless we can find a source neither can we say in the article that the problem is an inadequate terminology. Peter coxhead (talk) 17:36, 15 January 2014 (UTC)

Assessment comment[edit]

The comment(s) below were originally left at Talk:Ploidy/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

rated top as high school/SAT biology content - tameeria 15:03, 17 February 2007 (UTC) This article could benefit from pictures. I feel that diploid and haploid are important enough to have their own pages instead of redirecting here. In either case, a better explanation of diplont and haplont organisms and ploidy in biological life cycles would be helpful. - tameeria 19:51, 18 February 2007 (UTC)

Last edited at 19:51, 18 February 2007 (UTC). Substituted at 03:08, 30 April 2016 (UTC)