A (lengthy) article on BP Gentics

[jhall1468]

Actually a homozygous spider may have been produced; it's just that I’ve not seen anyone publicly claiming to have one yet 7 years into captive bred spiders. Hard to tell if that's because it really hasn't been produced (perhaps because not viable), hasn't had time to be proven homozygous through breeding yet, for some marketing reason (would it hurt or help spider prices?), or because homozygous spiders are in some way not publicly presentable.

True, but for the sake of the article I don't think any assumptions should be made. We look at the Banana, Pinstripe and Spider and no one has come out and said "I've produced a homozygous XXXXX". Then again, I think a LOT of people are too busy producing crosses to bother with such things. Even Super Pastels still seem to be relatively rare on the market.

With the popularity of Bee's these days, I imagine most people aren't breeding heterozygous Spiders together all that often. Although I'm sure the big breeders have... and if anyone has spiders it's them.

[RandyRemington]

It probably has more to do with the fact that since homozygous spiders don't look any differently than heterozygous spiders, most people out there don't want to look like a boob when the "homozygous" spider they claimed to have sires a clutch of normals.

But until someone's possible homozygous spider produces a bunch of only spiders we don't know for sure what homozygous spider look like. It's really hard to prove something by its absence. Just as I can't say for sure that spider is homozygous lethal by the absence of a publicly proven homozygous spider you can't say for sure it's dominant because of the absence of a publicly disclosed different looking potential homozygous spider.

What if it turns out that the homozygous eggs do hatch and produce a different looking or acting snake but it doesn't thrive and can't be bred to prove it's homozygous? With other potentially homozygous lethal morphs we've assumed a radically different looking animal is the homozygous without proving it so we could still reach closure on the spider genetics eventually. But what if the homozygous is only subtly different from the heterozygous ones but still consistently different and not capable of breeding and being proven?

Now if someone is selling homozygous spiders and they turn out not to be such I could see that being a problem but just coming out and saying “I think I have a homozygous spider, I’ll report back how the breeding results go” isn’t exactly going out on a limb. I’m thinking there has to be some other reason even if it is just that 7 years isn’t long enough with all the interest in outbreeding spiders.

[Mendel's Balls]

I really no longer think that ball pythons that are homozygous for the spider allele show embryonic lethality.

Why?

Not because there are not examples of pleiotropy in ball pythons or reptiles…..the superwoma (the pearl) demonstrate that genes influencing bp skin color can influence other body systems.

Not because there are no examples of homozygous lethal alleles in any snake species. The Jaguar gene in Carpet pythons appears to be homozygous lethal. “Supers” die shortly after birth. See http://www.naturalselectionreptiles....hersnakes.html and http://www.jaguarpython.com/docs/jaghist.htm.

Even before I knew of the examples above, neither of these counterarguments to the homozygous lethal hypothesis for Spiders held much weight for me. Why? Cause they never disproved the idea of homozygous lethal. It always remained a possibility for me.

But let’s look directly at the predictions of the homozygous lethal hypothesis for Spiders.

Good hypotheses and predictions are based off sound prior knowledge. In this case biological knowledge of the reproductive biology of Python regius.

The following prediction follows logically from the homozygous lethal hypothesis for spider ball pythons and prior biological knowledge.


Prediction: If the homozygous spider genotype (SS) is lethal, then we would expect ~25% chance of slugging in Spider x Spider crosses.


How did I arrive at this prediction? First, we expect ~25% chance of the homozygous genotype from a Spider (Ss) x Spider (Ss) crossing.

Second, let’s look at what would happen to those approximately 1 in 4 chance homozygous spiders if they were embryonic lethals.

In ball pythons, fertilization occurs after ovulation in the infundibulum, an anterior portion of the oviduct .

“Prior to ovulation the growth of the follicles can be reversed and the follicles can be reabsorbed by the ovary. After ovulation there is no mechanism in the body to reabsorb the eggs—once the follicles are ovulated, in one shape or another, something is going to be laid.” See the following link off of kingsnake for more info and the quote. Also special thanks to our own Infundibulum Inspector (xdeus).

So if the homozygous lethal story stands up we would expect that those homozygote that failed to develop due to their genotype would produce nonviable eggs (slugs).

As far as I know there is no known higher rate of slugging from Spider x Spider crosses. If there is no higher rate of slugging, then it seems to me that we must reject the homozygous lethal hypothesis of spiders. If I am wrong or ignorant of some fact, please let me know.

SO what is going on with spiders? Hard to say…..these things take time to work out.

One idea is that perhaps there are homozygous spider adults, but perhaps they are the spiders that fail to reproduce. It could be that the homozygous spiders (SS) don’t have what it takes to produce good eggs and/or sperm. Are such pesky, dud parents more frequent to anyone’s knowledge in spiders?

[RandyRemington]

Thanks!

So what is the definition of homozygous lethal? It was once suggested to me that the definition could be as broad as not being capable of reproducing. Does the woma/pearl qualify? Maybe there is a better term as the "lethal" part certainly seems to imply death and not just not being capable of it's biological imperative.

I do believe that at one point there was a post by someone in a large spider breeding camp that the spider X spider clutches didn't tend to slug any more than other ball pythons. I don't think any actual numbers or sample size was given. I still wouldn't rule it out as even normal ball pythons have been known to slug at rates that could compare to a homozygous lethal situation. But if you look at published large samples of non spider X non spider breedings like on Ralph Davis' breeding records pages it does seem the "normal" rate of slugs could be misleading as it's more often an all or nothing thing (some clutches totally bad but many others totally good rather than a steady high slug rate in all clutches). But I still question if homozygous spider eggs didn't hatch if it would be dismissed as a normal slug rate. It would take a pretty good sample size of spider X spider breedings and careful records to "prove" a trend if homozygous spider eggs don't hatch.

I also wonder if the homozygous spiders did hatch but where less perfect in some way like the pearl if we would hear about it. The pearl was the first reported cb white ball python so was very exciting to the community but unfortunately the lesson learned may have been to be much less forthcoming with information about any potential problems. If there are a couple similar projects now they might be sold for years before the details are publicly disclosed.

[Mendel's Balls]

From Cornell University Dept. of Animal Science:

embryonic lethal genotype: Genotype whose expression results in the prenatal death of the individual possessing it.

lethal genotype: Genotype whose expression results in the death of the individual possessing it.

Note lethal alleles or genotypes just cause a premature death. That death does not need to occur during embryonic development or childhood. Huntington disease typically causes a slow and sad decline to death in middle age. You only need one copy of this allele to get the diease. Hence, its classified as a autosomal dominant disorder.