Genetics/Morph FAQ

[Serpwidgets]

Ya, I know what you mean Zach. LOL

Recessive, codominant, dominant are relationships between two alleles. It's not necessarily the relationship between one mutant and wild-type. It also includes the relationship between any two mutants.

If you were to say "stripe is codominant" it would be assumed that the other gene it's being compared to is the wild-type, which is what I think Zach is saying. But at the same time it doesn't mean that the only "truly codominant" genes are those that are codominant to their wild-type allele.

 

[Paradigmboas]

Thanks.

You missed a stimulating chat tonight in the lobby where I was told that Salmon is not dominant, but incomplete dominant since super salmon x normal will give you some super salmons, salmons and normals in the group.

ROFL!

Imagine that, a trait being dominant, yet that particular snake not passing along any genes, or both copies to produce a homozygous snake!

Sigh. You need to come out with that all species genetics book, Chuck. Either that, or go teach those boas guys genetics one night. I had some lovely choice language thrown at me---it was good times.

Below is what is being taught in biology these days. Why is it wrong? :shrugs:
It was what I was taught in biology too. Have I been mis-informed? :shrugs:


Intermediate Expression

Blending can occur in the phenotype when there is incomplete dominance resulting in an intermediate expression of a trait in heterozygous individuals. For instance, in primroses, red or white flowers are homozygous while pink ones are heterozygous. The pink flowers result because the single "red" allele is unable to code for the production of enough red pigment to make the petals dark red. Red is homozygous dominant, pink is heterozygous, and white is homozygous recessive for the gene that controls color in primroses. Another example of an intermediate expression is the pitch of human male voices. The lowest and highest pitches apparently are found in men who are homozygous for this trait (AA and aa), while the intermediate range baritones are heterozygous (Aa).
If Mendel were given a mommy black mouse & a daddy white mouse & asked what their offspring would look like, he would've said that a certain percent would be black & the others would be white. He would never have even considered that a white mouse & a black mouse could produce a GRAY mouse! For Mendel, the phenotype of the offspring from parents with different phenotypes always resembled the phenotype of at least one of the parents. In other words, Mendel was unaware of the phenomenon of INCOMPLETE DOMINANCE.
Incomplete Dominance is the form of an example like so:

RED Flower x WHITE Flower ---> PINK Flower.
Or like mixing paints, red + white will make pink. Red doesn't totally block (dominate) the white, instead there is incomplete dominance, and we end up with something in-between.

Codominance

Two alleles can also be codominant. That is to say, BOTH are expressed in heterozygous individuals.
First let me point out that the meaning of the prefix "co-" is "together".
Cooperate = work together. Coexist = exist together. Cohabitat = habitat together.
An example of this is people who have an AB blood type for the ABO blood system. When they are tested, these individuals actually have the characteristics of both type A and type B blood. Their phenotype is NOT intermediate between the two.
In COdominance, the "recessive" & "dominant" traits appear together in the phenotype of hybrid organisms.
With codominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together.
Remember are example of the gray mouse above? In this case if the white gene and the black gene are codominant with respect to each other the f1's will have both black AND white hair...but no gray.
You can think of co-dominance as a screen door with each hole in the screen being filled with either a black or white but NO gray (or being filled with either A or B in the case with AB blood type. They exist side by side but do not blend. If they blended we would have a third blood type C and therefore a incomplete dominance.)
And you can think of incomplete dominance as black and white paint that has been blended all together to make a third color...gray.

 

[Serpwidgets]

I'm just pointing out that when you call Motley and Stripe codominant, you may want to indicate that it is recessive to wild-type, as you did with Ultra in Post #13.

I agree with this, except that I would say motley is dominant to stripe. :grin01:

 

[Serpwidgets]

Below is what is being taught in biology these days. Why is it wrong? :shrugs:
It was what I was taught in biology too. Have I been mis-informed? :shrugs:

You can think of co-dominance as a screen door with each hole in the screen being filled with either a black or white but NO gray (or being filled with either A or B in the case with AB blood type. They exist side by side but do not blend. If they blended we would have a third blood type C and therefore a incomplete dominance.)
And you can think of incomplete dominance as black and white paint that has been blended all together to make a third color...gray.

Yes they teach this in biology classes, but it's splitting hairs. This is like arguing that pi to 100 digits isn't "really" pi because you can also calculate it to 200 digits.

The point being made with the word codominant is that there are three possible phenotypes instead of two. Whether or not the third phenotype is a blending of the two or the simultaneous expression of both is not of major importance.

If A is codominant to a then Aa is a different phenotype than AA and aa. If you cross Aa to Aa then your outcome is a 1:2:1 split of the resulting phenotypes.

If A and a are incomplete dominant then Aa is a different phenotype than AA and aa. If you cross Aa to Aa then your outcome is a 1:2:1 split of the resulting phenotypes.

Notice how the two are, for all practical purposes, the same. The only real difference between them is the answer to the question, "what does the third phenotype look like?" In that case, you still would have to describe that third phenotype to someone who didn't know, because the "pink" flower might be almost completely red, and the mouse with black and white hairs might be an essentially black mouse with only have a handful of white hairs. So it doesn't really answer this question in itself, or provide any information of practical value any more than if you just said, "they're codominant to each other."

 

[Shep151]

I agree with this, except that I would say motley is dominant to stripe. :grin01:

In other words: A motley can be -for lack of a better term- "het stripe", but a stripe cannot be het Motley. Correct?
This is the little portion of the theory that Motley and Stripe are "simply" co-dom that keeps me holding it as plausible, despite the fact that my het Motleys produced M/S and Mots. The male produced ONLY Motleys when bred to a different female, so maybe I should keep the pair and breed them to stripes. If the theory is sound, one of the Anery "het Motley" should parent a clutch of stripes and normals and the other should have a clutch of mots, M/S, and normals, right? How much has this theory really been tested? Enough to make this small study insignificant (hopefully)?

 

[Serpwidgets]

In other words: A motley can be -for lack of a better term- "het stripe", but a stripe cannot be het Motley. Correct?
This is the little portion of the theory that Motley and Stripe are "simply" co-dom that keeps me holding it as plausible, despite the fact that my het Motleys produced M/S and Mots. The male produced ONLY Motleys when bred to a different female, so maybe I should keep the pair and breed them to stripes. If the theory is sound, one of the Anery "het Motley" should parent a clutch of stripes and normals and the other should have a clutch of mots, M/S, and normals, right? How much has this theory really been tested? Enough to make this small study insignificant (hopefully)?

I'm going on these as a basis of the idea that stripe is recessive to motley:
(Note that by "stripe" I mean the classic 4-lined stripe, and not the pinstriped motley type. )

1- I have never heard of a stripe being proven het for motley.

2- Snakes that are definitely stripe/motley genotype (because they have a homozygous striped parent) can be completely typical-looking motleys.

3- Snakes that are typical motleys (and proven het for stripe) can throw striped offspring.

(Yes, there's somewhat circular logic behind it, by assuming that all stripes are homozygous, but it's the best info there is so far and they are reasonable assumptions.) Honestly I think it's possible that stripe is not always 100% recessive to motley. But the most practical way to describe it (for now) is that way.

So yeah, I'd say you can have a motley het stripe. What that means to me is that it's genetically motley/stripe and it has a motley phenotype. (What else could it mean?)

 

[E. g. guttata]

I'm going on these as a basis of the idea that stripe is recessive to motley:
(Note that by "stripe" I mean the classic 4-lined stripe, and not the pinstriped motley type. )

1- I have never heard of a stripe being proven het for motley.

2- Snakes that are definitely stripe/motley genotype (because they have a homozygous striped parent) can be completely typical-looking motleys.

3- Snakes that are typical motleys (and proven het for stripe) can throw striped offspring.

(Yes, there's somewhat circular logic behind it, by assuming that all stripes are homozygous, but it's the best info there is so far and they are reasonable assumptions.) Honestly I think it's possible that stripe is not always 100% recessive to motley. But the most practical way to describe it (for now) is that way.

So yeah, I'd say you can have a motley het stripe. What that means to me is that it's genetically motley/stripe and it has a motley phenotype. (What else could it mean?)

So if this is the case, wouldn't it be more proper for motley to be m^S or m^M instead of m^m? I mean, in this case, it almost sounds like, though motley and stripe lie on the same locus, stripe is recessive to motley. Just a thought......

 

[Serpwidgets]

So if this is the case, wouldn't it be more proper for motley to be m^S or m^M instead of m^m? I mean, in this case, it almost sounds like, though motley and stripe lie on the same locus, stripe is recessive to motley. Just a thought......

The symbol is capitalized, unless it is recessive to the wild-type. Since motley is recessive to wild-type, the symbol is m^m.

(Use the HTML tags for sup and /sup, there aren't any for vb code. )

 

[Serpwidgets]

Aww aww, you beat me to the edit button. LOL

 

[E. g. guttata]

The symbol is capitalized, unless it is recessive to the wild-type. Since motley is recessive to wild-type, the symbol is m^m.

(Use the HTML tags for sup and /sup, there aren't any for vb code. )

I thought that m would indicate that the gene is recessive to wild-type, while ^M would indicate that it is dominant to another recessive gene?? Now I'm starting to get lost. LOL!

 

[Serpwidgets]

No need to get lost, just remember that the reference is always to the wild-type allele. :santa:

What if you have the albino locus where there's this:
· Normal (Dominant to amel and ultra, codominant with hyper)
· Amelanism (Recessive to normal, dominant to hyper, codominant with ultra)
· Ultra (Recessive to normal, codominant with amel, codominant with hyper)
· Hypermelanism (Codominant with normal, recessive to amel, codominant with ultra)

How would you indicate all of those relationships with simple symbols? :crazy02:

It would be nice if that could be incorporated into a simple symbology, where you could tell how every allele related to all others just by comparing symbols. But I don't think it's very practical, and I've never seen one used before. The trick is that there are going to be loci where there are plenty of mutant alleles. At the albino locus in mice, there are six or seven mutants, plus the wild type. Some alleles can be dominant, codominant, and recessive, depending on which other allele you are comparing it to, so the default reference is to the wild-type since there is always a wild-type.