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As far as I know, humans have 23 pairs of chromosomes, each one which contains a particular amount of genes. But in the "last" pair, men have a XY pair chromosome, and women have a XX pair chromosome. Does the missing "leg" of the XY pair make men to have fewer genes than women, and if so, how many genes do each sex have?

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    $\begingroup$ No a larger size human will have more genes:) $\endgroup$ – JM97 Mar 21 '17 at 2:34
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    $\begingroup$ Men do have more genes than woman. As I said in this comment, there is a consensus among geneticists/molecular biologists regarding the proper definition of gene and allele, which are not synonyms. Therefore, men have more genes than women (since men have all the genes women have plus the genes in the non-homologous region of Y chromosome), while women have more alleles than men. $\endgroup$ – user24284 Mar 21 '17 at 12:12
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    $\begingroup$ Also, regarding JM97 comment above: one human somatic cell, 10 human somatic cells or 500 human somatic cells have the same number of genes. $\endgroup$ – user24284 Mar 21 '17 at 13:15
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    $\begingroup$ Genetic issues, just as dichromatism, which is more common in men because a gene for trichromatism is found on the 23rd chromosome, is a good example of a sex chromosome dependent gene, so my assumption is that these differences mean a difference in number of genes. $\endgroup$ – fredsbend Mar 21 '17 at 17:45
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It is true that the Y chromosome is shorter than the X chromosome and that there are more genes on the X chromosome.

Do men have fewer genes?

One could (mis)understand three things in the expression "number of genes".

  1. Number of gene copies (see Copy Number Variation)
  2. Number of genes
  3. Number of alleles

Thanks to @GerardoFurtado for correcting my semantic in the comments.

1. Number of gene copies

From the statement that there are fewer genes on the Y chromosome, one can conclude that men have fewer genes copies than woman.

This is the intuition the OP seemed to have.

2. Number of genes

Men also have an X chromosome. So men have the standard genes present on the X chromosome (but they only have a single copy of it while women have two copies; btw you might be interested in dosage compensation).

Because women do not have a Y chromosome and because there are a number of genes on the Y chromosome that are not present on the X chromosome, men have genes that female don't have at all. Therefore women have fewer genes than men.

3. Number of alleles

There is not much reason to expect that one gender would be more heterozygote than the other at autosomes (=non sexual chromosomes). Some may hypothesize that women may have more heterozygosity than men if there is stronger selection among sperm than among ovules or things like that but let's not get down this complicated path.

One one hand women have more gene copies and therefore might experience more heterozygosity, one the other hand, men have more genes and would therefore eventually carry more alleles. I don't know which side wins!

Did you mean number of genes per cell or per individual?

So far I assumed you were interested about the number of genes (or gene copies) per cells but if you want to compare whole individuals than it is a different story!

Men are on average taller and therefore have more cells. Therefore if you compare the body-wide number of gene copies, women will have fewer gene copy on average (Thanks to @JM97 comment).

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  • $\begingroup$ For what I've read online, it isnt very clear how many genes the human have? According to this , counting the case of a human with XY chromosome, a human would have 31185 genes. But is it reliable or an aproximation? And how many it would be for a human with XX? es.wikipedia.org/wiki/Genoma_humano $\endgroup$ – Pablo Mar 20 '17 at 23:30
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    $\begingroup$ This is an entirely different question. You might want to post it on a separate post. But I can give you some hints here. I don't know a whole lot about the details of the human genome project but a big issue in counting the number of genes has to do with agreeing on what we call a gene. Estimates of protein-coding genes I am used to tend to be around 20k genes rather than 30k (See for example Church et al 2009 or Clamp et al. 2007). $\endgroup$ – Remi.b Mar 20 '17 at 23:42
  • $\begingroup$ Your wikipedia article does not cite any reference so I can't tell much about the meaning and validity of these results. The number they cite by the way is 32185 (not 31185). As a side note, I find the english wikipedia often more complete and more proof read than wikipedia in other languages (but I don't speak spanish and never go on the spanish wikipedia). $\endgroup$ – Remi.b Mar 20 '17 at 23:45
  • $\begingroup$ yes, it's true, english wikipedia is more reliable, but I just found that article there. $\endgroup$ – Pablo Mar 20 '17 at 23:51
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    $\begingroup$ I disagree with this answer, @Remi.b. Of course definitions depend on several factors, but it seems to me that there is a general consensus among geneticists/molecular biologists regarding the difference between a gene and a allele (thus, "number of genes" has a clear meaning and doesn't depend on what one meant). That being the case, the answer is unambiguous: men have more genes than women, while women have more alleles than men. $\endgroup$ – user24284 Mar 21 '17 at 11:28
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Note : the number of genes evolves. For who is interested and can understand french, heres a link speaking, in a short way, about that, and about the eventual disappearence of the y chromosom in human genom:
http://planet-vie.ens.fr/content/chromosome-y-humain
And a link about the inactivation of one of the X chromosom in women genom (corpuscle of Barr) : http://www.snv.jussieu.fr/vie/dossiers/kx/kx.htm

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  • $\begingroup$ @blacksun Shall we use the edit function and add this text to your other answer? I also requested the merge of both accounts into one - so you will can edit your own answer as well as having all your reputation in one account. $\endgroup$ – Chris May 16 '17 at 11:26
  • $\begingroup$ To Chris : in a certain way, this answer "number of genes evolves", is self sufficient, I think. But of course, the links I posted may disappear, and they are in french, sorry for that. If I find time for, I'll try to find english references, and sum up those references $\endgroup$ – Blacksun May 16 '17 at 11:34
  • $\begingroup$ To Tyto alba :I'm in fact the author of both answers ... I didn t participate for a while, because I lost the link to this subject, which I fall on working on very different things - and answering at first like on the very generalist forum I came from, thinking it was of same kind.. $\endgroup$ – Blacksun May 16 '17 at 11:34
  • $\begingroup$ It might take a few hours until this happens, depending on when the community manager team has time for that. $\endgroup$ – Chris May 16 '17 at 11:37
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    $\begingroup$ @Tyto alba Thanks Tyto alba, I'll try to remember that in the future ^^ $\endgroup$ – Blacksun May 16 '17 at 11:53
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As @GerardoFurtado noted in his comment, males have more genes since there are genes unique to the Y chromosome, like SRY. Of course, the fact that males only have a single X chromosome means that males will only have a single allele of each gene encoded by the X chromosome, while females have two alleles for each gene they have.

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As Remi.b said, there are different definitions of what a gene is. I found some more sources, if I understand correctly, according to the table in this wikipedia article with Data source of Ensembl genome browser release 87 https://en.wikipedia.org/wiki/Human_genome, a male human would have 14600 "pseudogenes" and a female human would have 14800 "pseudogenes" in each cell, and according this another table https://en.wikipedia.org/wiki/Chromosome#cite_note-26 , a male human would have 21000 genes and a female woman would have 21750 genes in each cell

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    $\begingroup$ Pablo, in fact there is no contradiction, first link speaks about 20 000 genes. But in those genes, there are some which are not activated, called pseudogenes... $\endgroup$ – Blacksun May 16 '17 at 10:26
  • $\begingroup$ I would add your comment to my post, but since I'm not very familiar with all of this, I might slightly or moderately missunderstand you, so may be you want to add this comment to your post, and make a reference to mine stating that there isnt a contradiction in both lists. If some of them are pseudogenes because they arent activated, why in the table they only have an entry for "pseudogenes" (and not for those which are activated and which would be called simply genes?) $\endgroup$ – Pablo May 16 '17 at 13:06
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Note - this is a very simple way to present things, and don't have the ambition to be a biology thesis.

Men do not have fewer genes than women, but fewer allels (variations of a gene); the allels on the x-y chromosome pair are not necessarily the same on the x and on the y (for men) or second x (for women), but they are for a part of same kind - same gene. It's like if, for a part, the y chromosome was broken, missing a bar to be an x.

One example of this is daltonism, linked to the xy chromosome pair.
Let's say that the daltonism allel is a corrupted existing allel (a variation of a gene).
To be a daltonist, a woman must have the daltonism allel on both of his x chromosomes - the daltonism allel is not a dominant allel, and if there is one corrupted allel on one x chromosome, but a normal one on the other x, the woman won't be a daltonist.

But a man is a daltonist only if his X chromosome do have the "corrupted" allel, because of the missing part of the y chromosome (compared to an x one).

If a woman has both allels, one "good" and one "corrupted", she will transmit it or not to his child, depending on which X chromosome she will give to this child.

If the father is a daltonist, he won't transmit it to his child if this child is a boy (he gives him his y chromosome genes and allels, not the x ones, and the boy takes an x from the mother, so he is xy).
But if his child is a girl, the father will transmit it to her (the girl take an x from the two of his mother and the only x from the father, so she is xx)

So, a child, to be a daltonist, must have at least a daltonist allel from his mother, no matter if the woman was daltonist or not (one x allel only corrupted or both).
Then, if this child is a girl, and is daltonist, it implies his father was daltonist too.
If it's a boy, no matter if the father is daltonist or not, he will be a daltonist as soon as his mother transmitted him a corrupted allel.

If the father is a daltonist, and if the mother has no daltonism allel at all, he will although transmit the allel to his daughters, who, while not being daltonists, will be able to transmit it to their own child.
In the same case (father daltonist, mother with no daltonism allel at all), if the child is a boy, he won't be a daltonist and won't be able to transmit it to his own child, etc, etc.

Remember, this is a simple way to present things, and do not pretend to be at the top of today's science vision, and even more not the truth - above the fact I'm not a biology specialist, every scientific that deserves this name won't ever be claimed to say the truth, something reserved for religions - and that's why science and knowledge, in general as well as for each people in the same spirit state, progresses ...

Last word, concerning the numbers of genes, according to Wikipedia - but you know that Wikipedia is not always the best source ;) - a human male has an estimated amount of 21 000 genes, and a woman, something between 0 and 50 fewer genes (800 genes on the x chromosome, 50 on the y one, but some of these are commons to both. How many, I don't know ...).
Sorry for the multiple edits, I try to give my 2 cents on this question after 2 days and a night without sleeping

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

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    $\begingroup$ can you add some references to your answer? $\endgroup$ – Vance L Albaugh Mar 21 '17 at 12:48
  • $\begingroup$ I'm a french guy, the references I took to check my knwoledge are in french ... Maybe, you can take a look at wikipedia with the words "color blindness", 'genetics' passage, and with the word "chromosome", 'human chromosome' passage, for a first approach $\endgroup$ – Blacksun Mar 21 '17 at 13:14
  • $\begingroup$ Note - I edited my answer, first speaking about eyes color, to explain the principles, bu t eyes colors genes are not on the 23rd pair of chromosome. I took so the daltonism, color blindness, but this exemple is still not perfect, just a simplifaction, as it seems that daltonism may comes from a gene mutation too, and his not only inherited ... But the principle for the inherited part is the good one, and illustrate enough, I think, the xy and number of genes discussion. Even if in fact, there is more complexity ... $\endgroup$ – Blacksun Mar 21 '17 at 13:27
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    $\begingroup$ As @GerardoFurtado noted in his comment, dominance applies to alleles, not genes. There's no such thing as "daltonism gene". $\endgroup$ – Dmitry Grigoryev Mar 21 '17 at 14:44
  • $\begingroup$ To Chris : I will edit it To Dimitry: right, that's what i called "kind of gene" and "genes" to simplify, the "kind" being in fact a gene, and the "gene" being an allel . I did proceed this way because number of people make the confusion. And I dont want to make here a biology thesis - and I m not able to ;) I dont want to make a biology thesis, and am not able to. But I can modify my comment i $\endgroup$ – Blacksun Mar 21 '17 at 16:33

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