# X and Y chromsomes in other mammals **URL:** \ **Category:** Factual Questions\ **Created:** [August 19, 2012, 2:55am UTC](https://boards.straightdope.com/t/x-and-y-chromsomes-in-other-mammals/631926 "2012-08-19T02:55:38Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Cub\_Mistress](https://avatars.discourse-cdn.com/v4/letter/c/ea666f/32.png) [@Cub\_Mistress](https://boards.straightdope.com/u/Cub_Mistress)\ **Post date:** [August 19, 2012, 2:55am UTC](https://boards.straightdope.com/t/x-and-y-chromsomes-in-other-mammals/631926/1 "2012-08-19T02:55:38Z")
In humans XX mean a female and XY means a male ( in general. I am aware there are other possible combinations) Does the same hold true for other mammals? Do they have X and Y chromosomes that determine gender? ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [August 19, 2012, 3:26am UTC](https://boards.straightdope.com/t/x-and-y-chromsomes-in-other-mammals/631926/2 "2012-08-19T03:26:09Z")
“The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects (Drosophila) and some plants (Ginkgo).” and for the [X0 system](http://en.wikipedia.org/wiki/X0_sex-determination_system): “This system is observed in a number of insects, including the grasshoppers and crickets of order Orthoptera and in cockroaches (order Blattodea). A small number of mammals also lack a Y chromosome. These include the Amami spiny rat (Tokudaia osimensis) and the Tokunoshima spiny rat (Tokudaia tokunoshimensis). Voles also have a form of XO determination in which both genders lack a second sex chromosome.” and: “The ZW sex-determination system is found in birds, reptiles, some insects and other organisms” ---
**Author:** ![Michael63129](https://avatars.discourse-cdn.com/v4/letter/m/3da27b/32.png) [@Michael63129](https://boards.straightdope.com/u/Michael63129)\ **Post date:** [August 19, 2012, 3:28am UTC](https://boards.straightdope.com/t/x-and-y-chromsomes-in-other-mammals/631926/3 "2012-08-19T03:28:04Z")
For most mammals, [they do use](http://en.wikipedia.org/wiki/Sex-determination_system#XX.2FXY_sex_chromosomes) a X/Y system to determine gender; a few however only use X chromosomes, with the male having only an X (not paired); there is even the rare case of no sex-specific chromosomes at all (based on this, rumors that males, and by extension the human race, will become extinct if the Y chromosome disappears are exaggerated). ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [August 19, 2012, 6:34pm UTC](https://boards.straightdope.com/t/x-and-y-chromsomes-in-other-mammals/631926/4 "2012-08-19T18:34:34Z")
> [@Michael63129](#): > > For most mammals, [they do use](http://en.wikipedia.org/wiki/Sex-determination_system#XX.2FXY_sex_chromosomes) a X/Y system to determine gender; a few however only use X chromosomes, with the male having only an X (not paired); there is even the rare case of no sex-specific chromosomes at all (based on this, rumors that males, and by extension the human race, will become extinct if the Y chromosome disappears are exaggerated). If the Y chomosome disappeared, why would males exist? You’d have women with or without Turner’s Syndrome. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [August 19, 2012, 6:35pm UTC](https://boards.straightdope.com/t/x-and-y-chromsomes-in-other-mammals/631926/5 "2012-08-19T18:35:23Z")
Sex determination is, to me at least, a really cool and interesting part of genetics. I find it fascinating that there are so many systems out there. But, yes, for the most part, mammals use the same XY system as we do, as has been stated. Drosophila was listed as another XY system, but since I study it, I have to point out that their XY system is rather different from ours. In humans, if you have a (functional\*) Y chromosome, you’re male. Period. XXY and XYY humans are male. In Drosophila (these are fruit flies, by the way), what matters is the ratio of X chromosomes to autosomes (chromosomes that aren’t sex chromosomes). Usually, all flies have two copies of the autosomes. 2 Xs give a ratio of 2/2, or 1, which translates as female. 1 X gives a ratio of 1/2, which translates as male. Note that the Y chromosome is utterly irrelevant. Flies that are XO, XY, XYY, or XYYY, etc, are all perfectly normal, happy, fertile males. Flies that are XXY, XXYY, etc, are all perfectly happy females. Now, what’s interesting is that you can make viable triploid flies, which have three copies of their autosomes. This lets you do funky things with the sex. Triploid flies with three Xs are normal females, with a ratio of 3:3, or 1. Having two Xs gives a ratio of 2/3, which is partway between female and male, and the flies look sort of half male and half female. And a triploid fly with one X, with a ratio of 1/3, is sort of a super-male. Again, the Y is irrelevant. ---
**Author:** ![Michael63129](https://avatars.discourse-cdn.com/v4/letter/m/3da27b/32.png) [@Michael63129](https://boards.straightdope.com/u/Michael63129)\ **Post date:** [August 19, 2012, 7:10pm UTC](https://boards.straightdope.com/t/x-and-y-chromsomes-in-other-mammals/631926/6 "2012-08-19T19:10:01Z")
> [@Saint\_Cad](#): > > If the Y chomosome disappeared, why would males exist? You’d have women with or without Turner’s Syndrome. I assume that if that ever happens, sex will be determined by some other method, otherwise, the human race would become extinct, no doubt about that. As I said, this has already happened in other species, with no devastating consequences: > [@](#): > > [Future evolution](http://en.wikipedia.org/wiki/Y_chromosome#Future_evolution) > > In the terminal stages of the degeneration of the Y chromosome, other chromosomes increasingly take over genes and functions formerly associated with it. Finally, the Y chromosome disappears entirely, and a new sex-determining system arises.[7] Several species of rodent in the sister families Muridae and Cricetidae have reached these stages,[17][18] in the following ways… > > …Primate Y chromosomes, including in humans, have degenerated so much that primates will also evolve new sex determination systems relatively soon, in about 14 million years in humans. By contrast, Turner’s Syndrome is a case where one of the chromosomes suddenly disappears with nothing to replace its functions, so it isn’t at all comparable. ---
**Author:** ![Lynn\_Bodoni](https://avatars.discourse-cdn.com/v4/letter/l/e47c2d/32.png) [@Lynn\_Bodoni](https://boards.straightdope.com/u/Lynn_Bodoni)\ **Post date:** [August 19, 2012, 7:43pm UTC](https://boards.straightdope.com/t/x-and-y-chromsomes-in-other-mammals/631926/7 "2012-08-19T19:43:48Z")
> [@](#): > > Flies that are XO, XY, XYY, or XYYY, etc, are all perfectly normal, happy, fertile males. Flies that are XXY, XXYY, etc, are all perfectly happy females. Just HOW does one determine whether or not a fly is happy? Do they smile? Do they frown? I will not be happy until I know this, as I wish to make as many unhappy flies as I can. I like bees, though, and I’m willing to make them happy. > [@](#): > > Sex determination is, to me at least, a really cool and interesting part of genetics. I find it fascinating that there are so many systems out there I was interested to learn that in chickens (and possibly other birds) it’s the hen that determines the sex, not the cock. I also found bee reproduction interesting. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [August 19, 2012, 8:27pm UTC](https://boards.straightdope.com/t/x-and-y-chromsomes-in-other-mammals/631926/8 "2012-08-19T20:27:53Z")
> [@Lynn\_Bodoni](#): > > Just HOW does one determine whether or not a fly is happy? Do they smile? Do they frown? I will not be happy until I know this, as I wish to make as many unhappy flies as I can. You can tell when they start buzzing around a pile of shit. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [August 19, 2012, 11:32pm UTC](https://boards.straightdope.com/t/x-and-y-chromsomes-in-other-mammals/631926/9 "2012-08-19T23:32:54Z")
> [@Michael63129](#): > > I assume that if that ever happens, sex will be determined by some other method, otherwise, the human race would become extinct, no doubt about that. As I said, this has already happened in other species, with no devastating consequences: > > By contrast, Turner’s Syndrome is a case where one of the chromosomes suddenly disappears with nothing to replace its functions, so it isn’t at all comparable. Part of what makes this whole thing interesting to me is the problem of defining what a sex chromosome actually is - or, more accurately, figuring out if a given chromosome is actually functioning as a sex chromosome. In humans, it’s not really the Y chromosome as a whole that’s important. It’s a gene on the Y called SRY (sex-determining region of the Y) that acts as a master switch for maleness. Over evolutionary time, other maleness-related genes have wandered onto the Y and stuck, but in early stages, it can be tricky to figure out how the chromosomes are determining sex. I’ve read papers in the past detailing species that seem to be in the middle of evolving new sex chromosomes. Cool stuff. ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [August 20, 2012, 12:14am UTC](https://boards.straightdope.com/t/x-and-y-chromsomes-in-other-mammals/631926/10 "2012-08-20T00:14:40Z")
IIRC it’s: y -\> SRY -\> male gonads (testes) form -\> hormones release that make you “male.” So the first 2/3 steps can go fine. But then your system has trouble accepting androgens like testosterone. So you develop testes, but the hormones aren’t accepted properly, so male systems don’t develop\*. This is Androgen Insensitivity Syndrome, most have XY buy appear female. My point is, like **Smeghead** has suggested, you can’t ultimately derive gender from XX/XY, and some abnormality at any point can change things. \*The pop-science quotation is that “we are all born female.” Not strictly true, we are born with both systems, but without any input from hormones etc., the male system(Wolffian) dies and the female(Müllerian) continues to develop.