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The Cultivars (morphs)/Genetics Issues Discussions about genetics issues and/or the various cultivars for cornsnakes commercially available.

king snake influence in tessera morph?
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Old 04-26-2015, 09:44 AM   #221
DuxorW
Quote:
Could this ratio reality be akin to male tri-colored cats being so rare and frail?
Calico is caused by a female being heterozygous for coat color alleles on her X chromosomes. Because of random X inactivation, each cell of the female only expresses one allele or the other, resulting in calico colors. Males have one X that is active all the time, so they cannot be heterozygous for the coat color alleles that cause calico, unless they have the configuration XXY instead of XY (the presence of two X chromosomes during development automatically triggers random X inactivation). In humans, XXY is called Klinefelter's syndrome and results in sterility and other issues.

I can't think of many plausible mechanisms that would prevent homozygous tesseras from being produced in the expected ratios if there isn't embryonic lethality, unless they involve prezygotic mechanisms (like for some reason a sperm carrying the tessera allele can't bind well to an egg carrying the tessera allele, such that the tessera egg almost always gets fertilized by non-tessera sperm instead...but this seems far-fetched). I guess someone needs to do a more rigorous analysis by holding back all the tessera offspring of tess x tess crosses.
 
Old 04-26-2015, 05:34 PM   #222
SODERBERGD
Tessera X Tessera

Quote:
Originally Posted by DuxorW View Post
Calico is caused by a female being heterozygous for coat color alleles on her X chromosomes. Because of random X inactivation, each cell of the female only expresses one allele or the other, resulting in calico colors. Males have one X that is active all the time, so they cannot be heterozygous for the coat color alleles that cause calico, unless they have the configuration XXY instead of XY (the presence of two X chromosomes during development automatically triggers random X inactivation). In humans, XXY is called Klinefelter's syndrome and results in sterility and other issues.

I can't think of many plausible mechanisms that would prevent homozygous tesseras from being produced in the expected ratios if there isn't embryonic lethality, unless they involve prezygotic mechanisms (like for some reason a sperm carrying the tessera allele can't bind well to an egg carrying the tessera allele, such that the tessera egg almost always gets fertilized by non-tessera sperm instead...but this seems far-fetched). I guess someone needs to do a more rigorous analysis by holding back all the tessera offspring of tess x tess crosses.
I wouldn't mind doing that this year (if I remember). I don't have eggs yet, but I bred a couple of those pairs. Since one of them is Tessera Het Scaleless Anery X same, I won't mind holding all of them back.

Thank you.
 
Old 05-18-2015, 03:05 PM   #223
Tavia
If you have a Tessera from a Tessera to Tessera pairing and you then breed it, how many Tessera offspring, with no non Tessera, would it have to produce to be considered a proven homo Tessera?
 
Old 05-18-2015, 03:51 PM   #224
DuxorW
Depends. You can do a statistical test that will tell you what the odds are of you getting all tessera offspring (say 15/15) by chance alone under the assumption that your potential homo tessera is in fact just heterozygous. We usually would reject the hypothesis that the animal is het tessera if there is only a 5% or less chance that we could get our result (ie all tesseras in a clutch of 15) by chance alone.

Indeed, the odds of getting 15 tesseras out of 15 eggs if your tessera parent is only het tessera is FAR less than 5%, so that result would be considered conclusive.
 
Old 05-18-2015, 04:44 PM   #225
Tavia
Good to know, thanks!
I have a clutch hatching now, only 12 eggs but the first 10 babies are all Tessera. Still have to see what the other 2 are. Unfortunately, the other pairing I tried with this Tessera male doesn't seem to have taken but a friend wants to borrow him this year for a pairing with one of his females. Hopefully he'll get a decent sized clutch from them and we can know one way or the other.
 
Old 05-18-2015, 05:09 PM   #226
DuxorW
Yeah, the odds of all tesseras out of 10 eggs is 0.001. So it's likely to be a super tessera but it only takes one normal to prove it wrong!
 
Old 05-19-2015, 08:01 AM   #227
Nanci
So what happened with the last two babies?????
 
Old 05-19-2015, 11:35 AM   #228
Tavia
Not great news, they are/were taking a long time to hatch, so I broke down and cut one a minute ago. It was DIE and I'm guessing had only been dead no more than 4 days, probably less. It was a perfectly formed Tessera, so at least I know what it was. Not sure why it didn't make it though. Not sure if that has anything to do with cause of death or not but the only weird thing about it was that it had a bunch of yolk in it's mouth and kind of appeared to have been trying to eat it. I took pictures but not sure if they are too graphic to post ...

Now trying to decide if I should cut the last one today or not. I will eventually, I'm too curious to know what's in there to not, it's just a matter of deciding when ...
 
Old 05-19-2015, 11:51 AM   #229
DuxorW
I'll bet money it's a tess, and hope it makes it for you.
 
Old 05-19-2015, 12:59 PM   #230
Tavia
I went ahead and cut it and it is a Tessera. I think it's alive, fingers crossed it stays that way! So we are 12 for 12 on this male's first clutch! I'd like a few more all Tessera babies out of him to be really sure but I'm going to assume for now that he is a homo Tessera.
 

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