Reptile & Amphibian Forums

dave

Here this may help:
Genetics 101

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Tosha

"Nihil facimus sed id bene facimus"

7.33.0 Ball Python (Harry and Fluffy and gang)
1.0.0 Angolan Python (Anakin Skywalker)
0.0.1 Green Tree Python (Verdi - yeah I know but my kids love the book)
0.2.0 Feline (Pippen and Pandora)
0.0.1 Desert Tortoise (Pope John Paul aka JP )
2.2.1 Fish (1,2,3,4)
0.0.2 frogs rescued from pool skimmer

Dominant/codominant/simple recessive -- these terms describe how the mutant alleles ACT. (For instance, a dominant allele would change the look of the snake if only one mutant allele is present. Whereas a simple recessive allele would change the look of the snake only if two mutant alleles are present.)

Heterozygous/homozygous -- these terms describe HOW MANY mutant alleles are present. (If only one mutant allele is present, then the animal is heterozygous. If two mutant alleles are present, then the animal is homozygous.)

Therefore, a Pastel (codominant) is heterozygous because it has one normal allele and one mutant allele, and the Super Pastel (codominant) is homozygous because it has two mutant alleles.

And this applies to all morphs.

Chris
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mean people suck

And before anyone nitpicks, this is the simple version. LOL

For instance, I know that heterozygous simply means two different alleles, and homozygous means two of the same. So technically I guess a Normal could be homozygous for Normal.

Who cares? Baby steps.

Chris =)
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mean people suck

>I know that heterozygous simply means two different alleles, and homozygous means two of the same.

Then why not give the newbies the correct definition?

>So technically I guess a Normal could be homozygous for Normal.

Exactly. And an animal with two different mutant genes is heterozygous. Example - a corn snake with a motley mutant gene paired with a striped mutant gene. A case of multiple alleles has not turned up in ball pythons yet, but it's just a matter of time.

Paul Hollander

"Then why not give the newbies the correct definition? "

Because I didn't realized that the "simple" definition (first attempt) wasn't as simple as the technical definition until AFTER I posted it. =)

Chris
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mean people suck

:

As I remember from genetics (which is not how we have been applying it to ball pythons and may be causing some confusion if someone looks up the techinical definitions)

dominate = always expressed

codominate = there is a chance of expression when combined with the normal gene (random which is actually expressed or in some cases the degree of expression), in people this is demonstrated by the rate of expression between blonde and red hair (with the intermediate expression being strawberry blondes)

recessive = needs to be combined with the same gene to be expressed

So technically, a codominate animal that does not demonstrate the trait may still carry the trait but an animal that does not demonstrate the dominate trait has no chance of carrying that trait (unless the dominate trait is recessive/codominate to a different trait (I do not think this has been discovered in ball pythons as of yet but as we go along, I think it will show up).
In the case of pastel which is reported to be a codominate trait, breeding the super (homozygous) for pastel to a normal results in all pastels. While this can occur in a codominate trait (as a statistical fluke), this is more indicative of a dominant trait (and is anecdotally supported by there are no reports of pastel siblings that are not pastels, throwing pastel offspring).

Some comments

Ed

Please explain it in simplest terms so that I no longer disagree with you.

Chris
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mean people suck

"In the case of pastel which is reported to be a codominate trait, breeding the super (homozygous) for pastel to a normal results in all pastels. While this can occur in a codominate trait (as a statistical fluke), this is more indicative of a dominant trait (and is anecdotally supported by there are no reports of pastel siblings that are not pastels, throwing pastel offspring)."

Are you saying that a Super Pastel (homozygous codominant) x Normal breeding experiment which produces all Pastels (heterozygous codominant) is a statistical fluke? I would think it would be a statistical certainty.

Please explain.

Chris
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mean people suck

It sounds to me like Ed is defining the difference between co-dominant and dominant as depending on if the hets are consistently mutants or not. I'm still thinking we have been using those terms correctly as depending on the difference between the hets and the homozygous.

However, whatever the correct terminology is I think the subject of consistency for the phenotypes per genotype is very interesting. I believe that some recessive mutations have co-dominant tendencies where the hets sometimes show (piebald in ball pythons and both green and granite in Burmese pythons). Maybe there are some co-dominant mutations with recessive tendencies where the hets sometimes look more normal? I've heard of some pastel siblings where the breeder wasn't sure if they where pastels or not. I've also seen a het ivory sibling that had some but not all the yellow belly characteristics. It will be interesting if we can hear back about any such animal's breeding results.

What I said snip "While this can occur in a codominate trait (as a statistical fluke), this is more indicative of a dominant trait (and is anecdotally supported by there are no reports of pastel siblings that are not pastels, throwing pastel offspring). " explained below

In a dominate trait, if the parent is homozygous and it is bred to a normal then all of the offspring will exhibit the trait even though they are all heterozygous.

In a codominate trait, a homozygous animal bred to a normal animal will have offspring that are heterozygous for the trait but the offspring may not exhibit the phenotype although there is a chance that all of the offspring may (the statistical fluke I was referring to) or may not.

For example a super pastel (homozygous) bred to a normal has 100% pastel babies. A pastel (heterozygous) bred to a normal has a mixture of normal and pastel offspring. As I understand it, breeding the normal offspring of a pastel-normal cross together does not produce pastels indicating that this is a dominate trait and not a codominate trait (other wise the normal appearing sibling cross could produce pastels).

With some animals what I think we maybe seeing are some variations in incomplete dominance of the genes. For example I have a het for orange ghost male (NERD line) that has gotten much lighter as he has gotten older when compared to a normal of the same age and some of his possible double het offspring (het albino x het orange ghost) are showing this distinct lightening.

Some more comments

Ed

>In a dominate trait, if the parent is homozygous and it is bred to a normal then all of the offspring will exhibit the trait even though they are all heterozygous.

True.

>In a codominate trait, a homozygous animal bred to a normal animal will have offspring that are heterozygous for the trait but the offspring may not exhibit the phenotype although there is a chance that all of the offspring may (the statistical fluke I was referring to) or may not.

No, all the offspring are heterozygous and will show an abnormal phenotype.

>For example a super pastel (homozygous) bred to a normal has 100% pastel babies. A pastel (heterozygous) bred to a normal has a mixture of normal and pastel offspring. As I understand it, breeding the normal offspring of a pastel-normal cross together does not produce pastels indicating that this is a dominate trait and not a codominate trait (other wise the normal appearing sibling cross could produce pastels).

Breeding the normal offspring of a pastel-normal cross together does not produce pastels. This indicates that pastel is either a dominant or codominant mutant gene and is not a recessive mutant gene. Breeding the normal-looking offspring of an albino-normal cross together does produce albinos, indicating that albino is a recessive mutant gene and not a dominant or codominant mutant gene.

A dominant mutant gene produces the same abnormal phenotype in both homozygous and heterozygous individuals. In other words, it requires a breeding test or knowledge of the pedigree to identify the genes.

A codominant mutant gene produces different abnormal phenotypes in homozygous and heterozygous individuals. In other words, the genes can be identified by looking at the animal. Pastel fits the definition of a codominant mutant gene.

Paul Hollander

Hi Paul,

It looks like either I misremebered what I was taught or was taught a very loose definition (which is why I said in the first post if I remembered correctly).

Thanks for the terms to check out.

Ed

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what you're saying is co-dom genes are heterozygous but you can't have a normal that is heterozygous for a c0-dom or dom trait.i think i understand now. i was confused because i'm thinking of hets in terms of simple recessive such as albino,piebald,etc.

>what you're saying is co-dom genes are heterozygous but you can't have a normal that is heterozygous for a c0-dom or dom trait.

A creature is heterozygous if the two members of a gene pair are not the same. If they are a pastel mutant gene and a normal gene, then the snake is heterozygous pastel and shows the pastel appearance. You can't have a normal-looking animal that is heterozygous for a codominant or dominant mutant gene.

But dominant and codominant mutant genes can also be homozygous. If the two genes in the pair are both pastel genes, then the snake is homozygous pastel.

Paul Hollander

spiders are doms,right? i posted a link yesterday to a genetics chart,kingsnake removed that thread-don't ask me why, but it used a spider as the example and it showed everything we're discussing but it confused me first because i didn't understand how doms and co-doms could be heterozygous,but what also confused me was it showed spider x spider produced a super spider which i thought did not exist. i think i saw a post here some time ago that said when a spider was bred to a spider they either had a clutch of slugs or the hatchlings died soon after emerging from the egg.

As far as I know, spider is either a dominant or a codominant mutant gene. Either nobody knows which it is, or them as do know aren't talking.

From the posts I've seen, a heterozygous spider x normal mating produces both spider and normal babies. This fits with spider being either a dominant or codominant mutant.

If spider is a dominant mutant gene, then heterozygous spider x heterozygous spider would (statistically) produce 1/4 homozygous spider, 2/4 heterozygous spider, and 1/4 homozygous normal. And the homozygous spiders and heterozygous spiders would look the same. A homozygous spider mated to a normal would produce all heterozygous spider babies.

If spider is a codominant mutant gene that is lethal when homozygous, then heterozygous spider x heterozygous spider would (statistically) produce 1/4 homozygous spider (slug or dead baby), 2/4 heterozygous spider (live), and 1/4 homozygous normal. There would be no homozygous spiders, and all spiders mated to a normal would produce some heterozygous spider and some normal babies. In this case, although there would be some slugs or dead babies from a spider x spider mating, not all would die. But slugs and dead babies appear every so often even in matings of two normal ball pythons. Are the slugs and dead babies in a spider x spider mating caused by the lethal effects of the spider mutant gene or by other causes? About the only way to tell, in my opinion, is to take a couple of dozen spider babies from spider x spider matings, mate them to normals, and get around twenty babies from each spider. Any that have normal babies in the mix are proven heterozygous spider. Any that have all spider babies have a greater than 99% probability of being homozygous spider.

Paul Hollander

HOMOsexual - two of the same sexes going at it

HETEROsexual - Two different sexes going at it

Homozygous - Two of the same gene (one from mom and Dad) for a given gene

Heterozygous (het) - Two different genes (on from mom and one from dad) One is morph and one isn't.

If it's dominant, it only needs one (het) to show up
If it's recessive, it needs both (homo) to show up

Jeremy
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Isn't it cooler that serpent's don't walk anymore?
(Genesis 3:14)

I'll give you the quick scoop.

1) Phenotype: Appearance of the animal, in a Co-Dominant or Dominant animal you will be able to tell if the animal has at least one of the genes based on the outward appearance.

2) Genotype: Genetic makeup of the animal. A heterozygous albino ball python has a phenotype of "normal" but a genotype of "het" albino.

Hope this helps.

Thanks for the e-mail...tried sending you a reply and it didn't work...
JC
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Isn't it cooler that serpent's don't walk anymore?
(Genesis 3:14)