Conjoined (Cephalopagus?) Twins that didn't make it *semi-graphic*

[William]

Albeit gross but it is interesting...

 

[KiKi]

omg poor little things

 

[Grinning Geckos]

Stina, I don’t know that I agree with you here, as the twins are not identical since their patterns are obviously different. The corn snake twins I hatched last year from the same egg (which did survive) weren’t identical either. I believe that is the case with human twins (vivipary) if one egg cell splits that the resulting offspring would be identical, but I think it’s different with reptiles (ovoviparity for leopard geckos & corn snakes).

I don't see how conjoined twins could be anything BUT "identical". This suggests to me that perhaps genetics are only part of what determines an exact pattern. I don't know enough about the roles of genes to say what exactly it might be, but the idea of symmetrically fused non-genetically identical embryos seems ... well, impossible to me. Any ideas?

 

[PaulSage]

Paul,

What project were these from? I noticed they were a little on the "normal" side. Either way, very weird!

They're Rainwater Blazing Blizzard x d.h. RWBB. Both adults were proven last year, but not to each other.

 

[StinaKSU]

an egg results from a single fertilized ovum, and conjoined twins are a result of incomplete fision of a single embryo (it's not generally believed that conjoined twins can result from the fusion of two embryos). Very early embryonic development is nearly identical across all animal species (fish-reptiles-mammals-birds) and monozygotic (including conjoined) twins result from fision of the embryo extremely early on in development. The differing patterns must be a result of something other than genetics... It could be something like calico cats where the pattern is developed by activation of genes somewhat at random during development (obviously not the same...but it could be smt similar).

 

[lazzara8478]

Wow! Thats amazing!

 

[BalloonzForU]

I'd had to say they are identical too, as their DNA would be the same. Even identical human twins do have some physical differences where you can tell them apart, birth marks etc.

 

[PaulSage]

an egg results from a single fertilized ovum, and conjoined twins are a result of incomplete fision of a single embryo (it's not generally believed that conjoined twins can result from the fusion of two embryos).

Don't you mean incomplete division? From the research I've been doing, that's one of the criticisms of the term "conjoined" for this occurence because the result isn't from anything "joining" together -- instead, it's the result from something not completely separating. Which, I agree with Shanti on, as I don't see how a splitting egg cell could be anything but identical because wouldn't one assume that they have the same DNA? I guess the pattern difference on the "conjoined" twins must somehow be affected by factors other than the DNA, but how different can those factors be? I mean, they were in the same egg for crying out loud! lol The corn snake twins I had were not visually identical either, but they weren't conjoined though. Interestingly, their most notable difference was a difference in pattern.

I'm not arguing or anything here, I'm just very intrigued by the whole thing and am curious as to what exactly "happens" when this occurs.

 

[StinaKSU]

fission is division.

 

[PaulSage]

Sorry, I thought you made a typo and meant fUsion.

 

[Sdaji]

Pattern and colour are controlled by genetics, but only to some extent. I've been working with reptile clones (mostly parthenogenetic Heteronotia) for a fair few years now and playing around with environmental influences to modify the phenotypes of different individuals within one clone is one thing I'm particularly interested in. I've been fortunate enough to have been able to play with large groups (up to 50 or so) or reptiles which have all been genetically identical to one another. They all have different scalation, different patterns and to some extent different colours (colours vary according to age, season, reproductive state, stress/health status, etc, and can change significantly within minutes or even seconds, so it's difficult to characterise). Scalation is remarkably variable between different individuals with the same phenotype and seems to be fairly strongly influenced by early incubation temperature. Pattern seems to be quite difficult to control, or at least I haven't yet figured out what the important environmental variables are in this respect. The Heteronotia geckoes I've been playing with are possibly quite different from Leopard Geckoes, which I have no first hand experience with, but I have no doubt at all that things such as pattern and scalation will never be identical between Leopard Gecko clones. I expect that pattern in geckoes (as with most reptiles) is very much like finger prints in humans. There is a genetic component which has some control over certain characteristics of the pattern, but there is also a chaotic component and possibly an environmental component as well. The finer details are almost entirely chaotic.

The Siamese twins I mentioned, which sat in my lab area during my honours year were not identical in pattern or scalation, but without a shadow of a doubt they were clones (their mothers were obligate parthenogens).

It has been speculated that in snakes, twinning usually occurs when two ova are shelled together (so really, they are just two eggs within one shell), although I tend to believe otherwise. In this case, it is a safe bet that the twinning has occurred through embryonic fission, as otherwise there would have been three eggs in total.

 

[StinaKSU]

In this case, it is a safe bet that the twinning has occurred through embryonic fission, as otherwise there would have been three eggs in total.

Twinning occuring via two ova being shelled together wouldn't cause conjoined twins either.

 

[robin]

Twinning occuring via two ova being shelled together wouldn't cause conjoined twins either.

unless during early development they somehow fused together

 

[OSUgecko]

If you look up pictures of animals that have been cloned in a laboratory situation (i.e., from another animal's body tissue) you will notice that none of them have the exact same color patterns as the parents... despite the fact that they all have the same genetics as their clone. Scientists have really only started to scratch the surface of color patterning genetics.

Stina mentioned calico cats... expounding slightly... Calicos are almost all female because the coloration is controlled by X-inactivation. Females have two functioning X-chromosomes, but each cell only needs one of them to be functioning at a time; the other is "inactive". Whichever X-chromosome is inactivated seems to be entirely random.

Calico coloring results from a gene found on the X-chromosome. There are dominant (orange) and recessive (black) alleles for this gene, and in order for the calico coloring to be expressed, BOTH of these alleles must be expressed simultaneously. This would normally be impossible, because the dominant gene would override the recessive (I know, I'm preachin' to the choir, most of you guys already know that). However, this works for cats because if one X-chromosome contains the dominant gene, and the other contains the recessive gene, they will BOTH be expressed randomly throughout the coat by X-inactivation.

Incidently, there is technically a way for calico males to exist... Klinefelter's syndrom causes males to have an extra X-chromosome.

Anyway, this is one aspect of coloration that is understood now, but most color patterns haven't even been touched in genetic studies. Someday maybe some researcher in a white lab coat will figure everything out... sure hope it won't be me!! (I'm REALLY getting tired of white lab coats and pipettes... that's what I get for working in a biochem lab)

 

[PaulSage]

Pattern and colour are controlled by genetics, but only to some extent. I've been working with reptile clones (mostly parthenogenetic Heteronotia) for a fair few years now and playing around with environmental influences to modify the phenotypes of different individuals within one clone is one thing I'm particularly interested in. I've been fortunate enough to have been able to play with large groups (up to 50 or so) or reptiles which have all been genetically identical to one another. They all have different scalation, different patterns and to some extent different colours (colours vary according to age, season, reproductive state, stress/health status, etc, and can change significantly within minutes or even seconds, so it's difficult to characterise). Scalation is remarkably variable between different individuals with the same phenotype and seems to be fairly strongly influenced by early incubation temperature. Pattern seems to be quite difficult to control, or at least I haven't yet figured out what the important environmental variables are in this respect. The Heteronotia geckoes I've been playing with are possibly quite different from Leopard Geckoes, which I have no first hand experience with, but I have no doubt at all that things such as pattern and scalation will never be identical between Leopard Gecko clones. I expect that pattern in geckoes (as with most reptiles) is very much like finger prints in humans. There is a genetic component which has some control over certain characteristics of the pattern, but there is also a chaotic component and possibly an environmental component as well. The finer details are almost entirely chaotic.

The Siamese twins I mentioned, which sat in my lab area during my honours year were not identical in pattern or scalation, but without a shadow of a doubt they were clones (their mothers were obligate parthenogens).

It has been speculated that in snakes, twinning usually occurs when two ova are shelled together (so really, they are just two eggs within one shell), although I tend to believe otherwise. In this case, it is a safe bet that the twinning has occurred through embryonic fission, as otherwise there would have been three eggs in total.

Wow. Thank you for that information :thumbsup:

 

[Sdaji]

No worries, Paul. Thanks for taking the time to read it

 

[Grinning Geckos]

I'm glad I stopped by ... I would have missed all of this! Great (and really interesting) info!

 

[Lottiz]

Yea, that was really something...Thanks for sharing Paul!

/Lottiz

 

[nwheat]

Very interesting, Paul! Sorry they didn't make it, but we sure have learned a lot from them!!

I think this new tidbit about nongenetic variation in pattern is fascinating!

 

[Intense Herpetoculture]

Didn't SF Gecko produce a conjoined baby a few years back?