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I was told some recessive homozygous to homozygous pairing/breeding will create lethal results!

Could this be a reason for some recessive mutations being weaker then others?

Anyone care to share experiences/opinions?

Wonder why no one's replying to this one....LOL

There ARE lethal alleles (genes) that when paired through inbreeding, or line breeding, cause deleterious effects.

Mostly this is obvious in higher order organisms such as mammals - it's your basic birth defect that everyone thinks of, created through incest. We also see genetic diseases in humans that result from inbreeding. Basically, what's happening is the inbreeding is allowing two identical ancestral genes or alleles to pair up, causing poor effects. Notice I didn't say "similar" genes, but identical ancestral genes. There's a difference between breeding a het to het of outbred recessives, or two lesser forms of a super (lower class reptiles) than there is inbreeding major relative higher class organisms (mammals), or long-term line bred lower classes (reptiles). Simply, the higher classes are more complex and there's more to be screwed up.

With the lower class reptiles, that we're mainly concerned with in this hobby, probably the largest example that comes to mind is breeding something like supertiger retics to supertiger retics. Or, another huge one is "bug-eyed" leucistic texas ratsnakes. I've never bred either of these two particular morphs. But I've definitely heard of poor viablity in resulting offspring (retics - super to super). And the appearance of the "bug-eyed" look in the rats came about through multiple generation inbreeding as well. It's not the "morph" itself that's making these babies poor. It's the constant inbreeding to create more of these morphs that are having negative effects on the babies. And some of these identical ancestral alleles that are allowed to pair back up are not visible to us (not color/pattern morphs)- they're under the surface.

I'm not trying to pi** on the ball python parade or the breeding of any morphs, as I enjoy breeding the morphs as well. I'm definitely NOT an anti-morpher. But we all need to keep in mind that these morphs we find appealing are really mutations that would normally lead to being "picked off" through natural selection in the wild. That's why morphs are so expensive - they're unique, and not many of them are in the wild. Natural selection keeps it in check - in the wild, the animals with the stronger gene pools will go on to produce more of their progeny, and albinos and other mutations have a greater chance of being eliminated. It really is a catch 22 however, because the appearance or features of wildtype phenotypes that occur today are also the product of mutations. BUT, they're mutations that were favored (camoflauge, physiology, etc.) and happened over thousand's of years vs. 10-20 years or less of what we've done in captivity. In captivity, you can have HEALTHY morph animals, but outbreeding HAS to be practiced to increase gene pools, and overall vigor health of the resulting offspring. It isn't as noticeable in lower class organisms as it is in higher class organisms, but over time and multiple generations, it definitely is going to have a similar negative effect on the animals. With reptiles, it might not be something as extreme as what we see with mammals (humans and others). But it could be shown in the form of weak babies, small litters, major and minor deformities. Ever see a one eyed burm or boa? Everyone has.

I'm not aware of two invidual different morph/mutations that when combined, create a "lethal" gene. If anyone experienced negative effects from that type of breeding it would probably have to be from a dbl hetero multiple generation line breeding, and be attributed from the introduction of each mutation's allele back to it's ancestral allele, and not necesarily the combo of the two.

To sum all this BS up, the key to healthy animals (whether wildtype OR morph phenos) is continued outbreeding. Sometimes it's not realistic when first establishing that morph. But it has to be done in at least later generations. It's not going to help line anyone's pockets by seeing a faster return on their investment by creating more morphs. But when you look at the big picture, the positive effects it has on the future of the hobby as a whole and eliminating the stereotypes of any specific morph being poor or lethal, is tremendous.

Just my 1000 cents.....

HellFire Reptiles

>I was told some recessive homozygous to homozygous pairing/breeding will create lethal results!

I worked for a while with a strain of mice with a mutant named jaundice. Heterozygotes looked normal. Homozygotes turned a pretty golden color and died within a couple of days after birth. There were no homozygotes available for breeding. The only way to keep the strain going was to identify the heterozygotes and use them.

Mutant genes can have a whole range of effects. Some seem to have no deleterious effects at all. Others have effects ranging from mildly deleterious to 100% fatal before birth. This is true for dominant, codominant (AKA incomplete dominant), and recessive mutant genes. Though the worst effects are not caused by dominant mutants because the creatures that have that sort of lethal dominant mutant are all dead.

But environment can also be deleterious. An incubator thermostat that goes haywire and cooks the eggs is just as fatal as a lethal gene. Then there are more insideous things, like stress and vitamin deficiencies, that affect our captive animals. Genetics plays a part, but environment is in there pitching, too.

Paul Hollander