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I have a biology degree, so I am pretty good at the genetics problems, but I have a question. Why do people group spiders into the codom family? I often read "spiders are a codom with no super form". Spider is dominant to normal and produces a 3:1 ratio of spiders to normals when a spider het normal is bred to a spider het normal. This is the exact same ratio as we would see if we bred a normal het albino to a normal het albino. This follows the simple recessive inheritance pattern to a key. Codoms should have three phenotypes (physical appearances) such as normal, pastel, super....and produces 50 percent pastel, 25 percent normal and 25 percent super. Am I missing something or are some people misrepresenting this morph?
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Thanks,
Amy
www.myboids.4t.com
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2.17 Normal ball pythons
1.0 Pastel ball pythons
0.0.1 Sinaloan Milk Snake
0.0.1 Plains Garter
0.1 Normal Kenyan Sand Boa
2.0 Anery Kenyan Sand Boa
1.0 Mid-Baja Rosy Boa
0.1 Leucistic Texas Rat
1.2 Dumeril's Boa
My list is too long, so I'll stop here!

Spider is dominant to normal and produces a 3:1 ratio of spiders to normals when a spider het normal is bred to a spider het normal.

How much spider X spider breeding data do you have to back that 3:1 ratio up? Have you seen the clutches at hatching time to count bad eggs/sluggs, typical looking spiders, and any odd ball hatchlings or dead in the egg?

If the sample size is large and the hatch rate is much higher than 75% and the ratio of phenotypic spiders to normals is much closer to 3:1 than 2:1 then you may well be right and spider may be dominant. It would still be uncertain until a homozygous spider is proven through breeding to a bunch of normal for spiders and producing a large number of only spiders and no normals.

However, given that 7 years into the spider project there is still noone publicly claiming to have a proven homozygous spider there is still the possibility that the homozygous spiders don't hatch or are in some way not publicly presentable. Would that technically be considered co-dominant situation?

I don’t think we have enough public information to close the case on spider genetics one way or the other yet.

>However, given that 7 years into the spider project there is still noone publicly claiming to have a proven homozygous spider there is still the possibility that the homozygous spiders don't hatch or are in some way not publicly presentable. Would that technically be considered co-dominant situation?

Sure. All you need is a 1:2:1 phenotype ratio when mating two spiders (with a spider mutant gene paired with a normal gene). A 1 dead (or unbreedable) : 2 spider : 1 normal ratio fills the bill. Dominant yellow (AKA lethal yellow) in mice is one of many possible examples where the homozygous mutant is lethal while the heterozygous type is obviously abnormal.

Paul Hollander

Thanks...I hadn't heard that there was a lethal gene in spiders. I agree that a lot of the spider genetics is still up in the air. The 3:1 ratio is theorectical anyways, I wish I could always produce 50% pastels to 50% normals haha!
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Thanks,
Amy
www.myboids.4t.com
----
2.17 Normal ball pythons
1.0 Pastel ball pythons
0.0.1 Sinaloan Milk Snake
0.0.1 Plains Garter
0.1 Normal Kenyan Sand Boa
2.0 Anery Kenyan Sand Boa
1.0 Mid-Baja Rosy Boa
0.1 Leucistic Texas Rat
1.2 Dumeril's Boa
My list is too long, so I'll stop here!

The spider mutation may BE a homozygous lethal allele of its gene or it may not be, it's just one of several possible explanations. Any dominant type (including suspected co-dominant) mutations where a mature breeding homozygous animal has not yet been publicly proven should be treated as possibly homozygous lethal until proven otherwise. It would be nice if they all worked out but it's not guarantied and as always the potential for reward caries risks.

I've actually seen most everyone refer to spider as dominant rather than co-dominant. The assumption is apparently that the homozygous spiders must be there in the undisclosed number of spider X spider breedings so far and look just like the heterozygous ones. You took that assumption a step further and predicted the 3:1 ratio of spider to normal offspring in a (het) spider X (het) spider breeding. Perhaps now that spiders are more affordable and more people are working with them more data will become available to the public to figure out with more certainty how the gene works.

If it does turn out to be homozygous lethal it will be difficult to “prove”. It’s very hard to prove something by its absence. Each year the proven homozygous spider becomes more conspicuous by its absence but there are always other possible explanations. Maybe it will show up the next year? If the full breeding results of spider X spider where available they might point to one or the other explanation but even then there would be the question as to if the sample size was large enough to prove anything. If the surviving hatchlings occur at a 2:1 spider to normal ratio rather than a 3:1 it might just be bad luck. If the hatch rate is higher then 3/4 of the clutch that might be good luck or something we don't understand about the python egg producing process.

We are always speculating. Even if you say that it is completely dominant and the homozygous spiders exist and look just like heterozygous spiders you are still speculating until one is proven homozygous. Even then you would have to decide how many spiders in a row a potential homozygous spider would have to produce bred to normals before you considered it proven homozygous. You should just consider all the possibilities we as a community can come up with to weigh your speculations.

>(snip) If it does turn out to be homozygous lethal it will be difficult to “prove”. It’s very hard to prove something by its absence. (snip)

I asked that question to a retired genetics prof I know. He's working on a similar problem in finches. He told me that he is planning on testing 21 possible homozygotes before calling his mutant lethal when homozygous.

>We are always speculating. Even if you say that it is completely dominant and the homozygous spiders exist and look just like heterozygous spiders you are still speculating until one is proven homozygous. Even then you would have to decide how many spiders in a row a potential homozygous spider would have to produce bred to normals before you considered it proven homozygous. (snip)

The probability of getting seven spiders in a row from a heterozyous spider x normal mating is 0.007. And the probability of getting 10 spiders in a row from that mating is a hair under 0.001. In other words, if an average clutch of eggs is six, then one average-sized clutch will identify most of the heterozygotes. Two clutches totalling 10 eggs or more should be enough, I think. But I don't expect a 99.9% probability homozygous spider to be taken off the breeding rolls after only two clutches.

Paul Hollander

Very interesting! The reason I posted my comments initially, was because I was curious to why many people refer to the spider as "dominant", but follow up with "a codominant with no super form". It sounded goofy to me. The ratios I mentioned were all "expected" ratios, and as you guys were saying we would need large numbers of spiders to really verify the inheritance pattern one way or the other. To prove my 3:1 ratios (or any ratios for that matter)...the Chi-square would certainly have to be dusted off, and quite frankly, I can barely afford one spider, so I'll have to wait for my answer haha!

Enjoy your evenings!
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Thanks,
Amy
www.myboids.4t.com
----
2.17 Normal ball pythons
1.0 Pastel ball pythons
0.0.1 Sinaloan Milk Snake
0.0.1 Plains Garter
0.1 Normal Kenyan Sand Boa
2.0 Anery Kenyan Sand Boa
1.0 Mid-Baja Rosy Boa
0.1 Leucistic Texas Rat
1.2 Dumeril's Boa
My list is too long, so I'll stop here!

>The reason I posted my comments initially, was because I was curious to why many people refer to the spider as "dominant", but follow up with "a codominant with no super form". It sounded goofy to me.

It is goofy. But there is a reason. Most herpers learn bits and pieces of genetics as they need it. The first mutants that showed up were recessive mutants, so they learned how to handle that. Then some codominant mutants showed up, and they learned how to handle that, more or less (often less). But no really good dominant mutants have turned up in snakes. They've all shown some variable expressivity and tended to get lumped in with the codominant mutants. Salmon in boa constrictors is a case in point.

If you really want goofy, look on some of the herp genetics web sites. A fair number use "codominant" where standard genetics would use "heterozygous for a dominant or codominant mutant" and "dominant" where standard genetics would use "homozygous for a dominant or codominant mutant".

By the way, the first codominant mutant in snakes was tiger in the reticulated python. The homozygous phenotype got named "super tiger", and "super" has stuck for most of the codominant homozygotes.

Paul Hollander

The "dominant form" for homozygous co-dominant is very unfortunate. I understand it even made it into one of the otherwise highly praised books. It would be nice if that could get corrected before it spreads further but if anything it seems to be gaining momentum as I saw another big breeder use it in the main ball forum recently.

Thanks guys! It is refreshing to read responses from such knowledgeable herpers! Thanks for all of the information! Also, very interesting about the retics!

Have a great weekend!
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Thanks,
Amy
www.myboids.4t.com
----
2.17 Normal ball pythons
1.0 Pastel ball pythons
0.0.1 Sinaloan Milk Snake
0.0.1 Plains Garter
0.1 Normal Kenyan Sand Boa
2.0 Anery Kenyan Sand Boa
1.0 Mid-Baja Rosy Boa
0.1 Leucistic Texas Rat
1.2 Dumeril's Boa
My list is too long, so I'll stop here!

By the way...while I was fishing the web I noticed Randy's genetics 101 at http://www.ballpython.ca/genetics_101.html

It is probably the best basic ball python genetics site I have been too, and completely answered my initial question...haha if only I found it sooner Too bad we can't "sticky" this website to the forum!

Good job!
-----
Thanks,
Amy
www.myboids.4t.com
----
2.17 Normal ball pythons
1.0 Pastel ball pythons
0.0.1 Sinaloan Milk Snake
0.0.1 Plains Garter
0.1 Normal Kenyan Sand Boa
2.0 Anery Kenyan Sand Boa
1.0 Mid-Baja Rosy Boa
0.1 Leucistic Texas Rat
1.2 Dumeril's Boa
My list is too long, so I'll stop here!

Thanks but I'm sure it could use some corrections too. It doesn't help that genetics terminology varies so much in usage between groups (i.e. snake keepers vs. fruit flies vs. rodents etc.).

However I do think it is important to keep the mutation type names like recessive, co-dominant, and dominant separate from the genotype names like heterozygous and homozygous. For example, pastel is considered co-dominant (it's arguable if that is the exact right term) and the mutation type doesn't suddenly change to dominant when you are looking at a homozygous pastel, it's just the genotype that has changed. Keeping the different ways of categorizing animals (mutation type, genotype, and phenotype) separate while understanding the relationships will help to avoid confusion.

>>However, given that 7 years into the spider project there is still........

It's way more than that Randy. The original spider was imported in 1989. Kevin bought it from Randy Buck of Superpets that year. That same year Tracy bought the original clown from Randy.

My money is on simple dominance for spiders.
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