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Some sources say that gametes are haploid, some say that they are diploid.

I'm confused.

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    $\begingroup$ Could you give a source that says gametes are diploid, or that zygotes are haploid? It is hard to tell what it is that's confusing you here; the answer to your question is normally an elementary Google/Wikipedia/biology textbook search away but presumably you're getting contradictory info somewhere, but if we don't know what that info is we can't help. $\endgroup$
    – Oosaka
    Apr 29, 2017 at 13:17
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    $\begingroup$ @ViaLo Can you please edit your question, rephrasing it and improving its wording? I just edited it to add the genetics tag, but I avoided any edit in the question itself because, if I did it, I'd end up substantially changing your own words. $\endgroup$
    – user24284
    May 1, 2017 at 11:16
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    $\begingroup$ @RozennKeribin despite zygotes never being haploid (since the very definition of haploid), it's possible to find diploid gametes: such gametes are diploid and haploid at the same time. $\endgroup$
    – user24284
    May 1, 2017 at 14:02
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    $\begingroup$ Well, @ViaLo, I edited the question removing the unnecessary (and confusing) parts, feel free to rollback if you want. $\endgroup$
    – user24284
    May 1, 2017 at 23:02

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Actually there is some confusion here, and that's quite excusable, because it's extremely common reading that monoploid and haploid are synonyms and have the same meaning. However, they are different terms. According to Hartl and Ruvolo (2012):

The potential confusion arises because of diploid organisms, in which the monoploid chromosome set and the haploid chromosome set are the same.

As we, human beings, are diploid organisms, it's easy to see why haploid and monoploid ended up being considered as synonyms.

However, a more precise terminology would be:

  • Monoploid: the total number of chromosomes in a single complete set of chromosomes (this does not change whether we are talking about a somatic cell or a gamete).
  • Haploid: half of the total number of chromosomes in a somatic cell. The haploid chromosome set is the set of chromosomes present in a gamete, irrespective of the chromosome number of the species.

That being said, diploid and haploid are not antonyms nor mutually exclusive terms. A cell can be diploid and haploid at the same time. Let's exemplify this with organisms that perform gametic meiosis:

Human beings have diploid somatic cells, with 46 chromosomes. When a somatic human cell perform meiosis, it produces haploid cells which are monoploid. Human gametes are haploid and monoploid.

In wheat (Triticum aestivum), somatic cells are hexaploid, having 42 chromosomes (that is, 6 full sets of 7 chromosomes). When a wheat cell perform meiosis (producing micro and mega spores, and later on gametes), it produces haploid cells which are triploid. Wheat gametes are haploid and triploid.

The same whay, a tetraploid organism would produce, by meiosis, a cell which is haploid and diploid. Thus, depending on the number of chromosome sets in the somatic cell of a given species, you can say that a gamete is diploid (as stated in this other answer).

In a nutshell, a gamete that was produced by meiosis (there are life cycles where the gamete is not produced meiotically) is always haploid, regardless the number of chromosome sets it has (which will determine if it is monoploid, diploid, triploid, hexaploid etc...).

Sources:

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It depends on the organism in question. (https://en.wikipedia.org/wiki/Polyploid#Examples)

Notice that the gametes carry half number of copies of the normal cells. As such a tetraploid organism will have diploid gametes.

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This is a confusing topic when it comes to polyploids. I don't believe the definition for haploid provided in the accepted answer is correct for all species.

Haploid refers to a cell or an organism that has only a single set of chromosomes - my interpretation is that it is only in a diploid organism such as a human that haploid means "half of the total number of chromosomes in a somatic cell", because diploid organisms produce haploid gametes.

A diploid human produces haploid gametes. A hexaploid produces triploid gametes.

I think the confusion in the accepted answer is that gamete means the same as haploid (which of course is true only for diploids, such as humans). The triploid gametes are not haploid. The definition in my answer supports that, and indeed if you search, other definitions state this also e.g. "Haploid describes a cell that contains a single set of chromosomes".

I should add, to answer the question, that the gametes are diploid for a 4n tetraploid organism - when the gamete is produced 2 of these go to one gamete, and 2 to other (diploid). It may be that the source you read was referring to a tetraploid organism.

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  • $\begingroup$ Welcome to Biology.SE. (+1) This is much better than the accepted answer, but I saw a few ways to make improvements. In particular, there were couple of statements that could cause confusion. The second of these I deleted since it wasn't necessary to make your point — while "genome" can be used to refer to the haploid set of chromosomes, it usually means all the chromosomes. $\endgroup$
    – tyersome
    Jan 13 at 18:51
  • $\begingroup$ Actually — it appears that we are both wrong and the accepted answer is OK. You can see this in the second sentence of the second link you provided where it says "The term haploid can also refer to the number of chromosomes in egg or sperm cells, which are also called gametes." This unfortunately means that haploid has two meanings that sometimes are in conflict — to be unambiguous we should use monoploid (and it seems to me, completely avoid haploid) ... Would you like to edit your post in light of this information? $\endgroup$
    – tyersome
    Jan 13 at 19:07
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Don't get confused by the number of chromosomes. Haploid refers to 1 set of chromosome, diploid refers to 2 set of chromosomes, triploid means 3 set of chromosomes. They don't represent the numbers of chromosome present on a set.

We human beings have 23 chromosomes on a single set. We are diploid organisms and thus all the cells of our body carries two set of chromosomes (thus 23*2=46). Our germ cells however are formed through meiosis cell division and thus they are haploid (23 chromosomes).

So, sperm cell carries 23 chromosome and egg carries 23 chromosome each. When they fuse, zygote is formed and as you can see, zygote carries 23+23=46 chromosomes. Zygote undergoes mitotic cell division and a complete human is formed. So, human zygote definitely is diploid.

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  • $\begingroup$ Does it mean ONE SET means 23 chromosomes (out of 46). $\endgroup$
    – Tanvir
    Jun 22, 2018 at 14:36
  • $\begingroup$ Yes, one set is 23. one set chromosomes are present in the germ cells like sperm and egg $\endgroup$
    – Anindya
    Sep 4, 2018 at 17:39
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Gametes must be haploid because they will be combining with another gamete. Sexual reproduction works to increase genetic diversity by having two haploid gametes combine to form a new organism that has a different combination of genes than either of its parents. The new organism has half the chromosomes from its mother and half from its father.

Source from Chromosomes and Meiosis Interactive

For example, in order for humans to reproduce, a sperm cell must fuse with an egg cell, producing a zygote that has a unique set of genetic information. If the gametes were diploid instead of haploid, the resulting organism would have too many chromosomes. By having two haploid gametes fuse together, it is ensured that the new organism will be genetically distinct and still have the correct number of chromosomes that it needs.

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  • $\begingroup$ Welcome to Biology. It is great that you are contributing to this site by answering questions but please try to read other answers for a given question before answering so that there is no redundancy. Redundant answers are not useful. Perhaps you should add some extra information that is not covered by other answers. $\endgroup$
    – WYSIWYG
    May 30, 2019 at 9:01

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