Talk:Ploidy

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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)

Contents

[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 approvial. Lefty 16:03, 2005 Mar 12 (UTC)

also Haplodiploidy. Lefty 16:08, 2005 Mar 12 (UTC)

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

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." 76.81.218.167 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 70.246.31.242 (talk) 04:41, 9 October 2007 (UTC)

[edit] looking away from diplontic organisms..

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 165.254.143.3 (talk • contribs) email address removed -postglock 06:59, 31 August 2006 (UTC)

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

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

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)

[edit] Euploidy

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.

[edit] Ploidy vs monoploid number?

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)

[edit] Homologous set

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)

[edit] Haploid

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)

[edit] Haploid and monoploidy contradiction

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 (talk • contribs) .

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

[edit] Males and Females in Haplodiploid Species

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)

[edit] Mixoploidy

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)

[edit] Monoploid v Haploid

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)