# Reptile Sex Chromosome System - XX/XY or ZZ/ZW?



## 9Red (May 30, 2008)

Just wondering if anyone knows which chromosomal sex determination system is usually* found in reptiles? 

Is it the XY system as usually found in mammals (XX for female and XY for male)?

Or is it the ZW system as seen in birds (ZW for female and ZZ for male)?

I was studying this the other night and the question popped up in my head as one would automatically assume its the XY system, but then birds are descended from reptiles, and they have the ZW system, so maybe this is part of their evolutionary heritage?

*I say usually as I know that in some species gender is determined by environmental factors such as temperature, and that other reproduce via parthogenesis.


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## Ssthisto (Aug 31, 2006)

In the animals that are chromosomally sex determined, I am pretty sure they're ZZ-male and ZW-female.

However, mammals are ALSO descended from reptiles


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## GlasgowGecko (Feb 23, 2008)

Ssthisto said:


> In the animals that are chromosomally sex determined, I am pretty sure they're ZZ-male and ZW-female.
> 
> However, mammals are ALSO descended from reptiles



This is infact true. An example to show this is parthenogenesis in Komodo Dragons can only create males.

Andy


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## Sarah1340 (Sep 14, 2008)

Aha! Just doing a paper on this for my zoology degree.

ZZ (male)/ZW (female) - snakes, some lizards
XY (male)/XX (female) - some lizards, some turtles

Crocodilians, most turtles and tuataras actually have no sex chromosomes, sex is determined for them purely by temperature and environmental factors.

Hope this helps


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## repkid (Nov 30, 2007)

Sorry to but in but what does parthenogenesis mean?


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## MrMike (Jun 28, 2008)

repkid said:


> Sorry to but in but what does parthenogenesis mean?


It is the production of offspring when only females are present. No male required. I wold assume this is why parthenogenesis in Komodos only produces males.


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## repkid (Nov 30, 2007)

So the female fertilises herself?


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## MrMike (Jun 28, 2008)

repkid said:


> So the female fertilises herself?


Yes, in a way. I'm no expert but basically yeah.


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## repkid (Nov 30, 2007)

So, in a way similar to an earth worm?


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## MrMike (Jun 28, 2008)

repkid said:


> So, in a way similar to an earth worm?


Similar, but I don't think exactly the same, don't earthworms completey reproduce asexually?


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## bothrops (Jan 7, 2007)

repkid said:


> So, in a way similar to an earth worm?


Not quite. Earthworm are hermaphrodites meaning they are both male and female. They have sex and exchange gametes (sex cells) but both parties go away from the meeting 'pregant' (in fact the fertilisation doesn't occur till later, but it is always the joining of gametes from two different individuals.

Parthenogenesis is the production of young from a single female with no gametes from any other organisms.

Cheers

Andy


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## repkid (Nov 30, 2007)

OK

Thanks you two for clearing that up!:2thumb:


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## Ssthisto (Aug 31, 2006)

And not all parthenogenic species produce all males - the ones that are actually exclusively parthenogenic are all female; it's just the ones that NORMALLY reproduce sexually that will pop out boys, by the sound of it.


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## GlasgowGecko (Feb 23, 2008)

Parthenagenesis is reproduction through genome duplication.
So If a female has the ZW chromosomes, duplication can create either ZZ or WW. WW can not survive, so ZZ is the only possible option. This leads to all males...

Though it is true, parthenogenesis does not create only males (in certain organisms). In this system, it is the only possible outcome.

Andy


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## snakeprint (May 29, 2008)

This discussion is scarily intellectual! I hadn't even considered that there was anything other than the XY system that we know in humans. How is W and Z different to X and Y? I'm guessing it's not the same thing just labelled a different letter? Genes fascinate me, although I know next to nothing about them!


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## Shellhead (Jan 4, 2008)

In the XY system the Y chromosome determins the sex.
In the ZW system the W determins the sex.
Im not sure as to why they are labled differently, maybe its something to do with what the DNA in the chromosome does.


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## eeji (Feb 22, 2006)

Sorry for being thick, but if in certain species if males are the only sex produced, where do the females come from?

---------------- When Eeji posted this, he was listening to: Orbital feat. Earth LeakageTrip - No Idea


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## Shellhead (Jan 4, 2008)

Nature tends to balence out the production of males and females (that being there is an equal chance of having a male and female, unless you are temperature controlling the incubation in some species). Im not sure if that would ever happen. Unless your talking about Parthenagenesis, then there are already females there, its only when the famale does parthenagenesis that it only creates males. The reason it does this is to create males to breed with. Would be abit crap for the female if it had another famale lol.


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## Ssthisto (Aug 31, 2006)

GlasgowGecko said:


> Parthenagenesis is reproduction through genome duplication.
> So If a female has the ZW chromosomes, duplication can create either ZZ or WW. WW can not survive, so ZZ is the only possible option. This leads to all males...


Unless of course you're talking about the all-female species - like the whiptail species that are exclusively female and lay eggs that are clones of themselves.



Shellhead said:


> In the XY system the Y chromosome determins the sex.
> In the ZW system the W determins the sex.
> Im not sure as to why they are labled differently, maybe its something to do with what the DNA in the chromosome does.


I'm pretty sure they're labelled based on what the chromosomes actually look like - an X chromosome is x-shaped; a Y chromosome is y-shaped.


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## Shellhead (Jan 4, 2008)

Thats what i would have thought, but then i dont know what the Z and W chromosomes look like.


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## GlasgowGecko (Feb 23, 2008)

The main difference here is that in the X-Y system, individuals with the Y chromosomes become males, two copies of X = females.
In the Z-W system, individuals with the W chromosome are female, and those with two Z chromosomes are male.
So the systems are effectively opposites of each other, hence the need to delimit the difference.

Whiptails are a very complicated subject, and although interesting probably warrant a thread of their own. Needless to say, something different is happening there to the example i mentioned above...

Andy


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## Shellhead (Jan 4, 2008)

Ahhh, that makes sence.
Cheers

Jacob


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