I just had an epiphany...

[Russ Lawson]

Ok, something that has never sat right with me since I started studying genetics when I first became really interested in ball python mutations around six years ago was the textbook definition and examples given for the term co-dominance. The first example was the roan cow, which basically appeared to be the same exact thing as incomplete dominance. The second textbook example of co-dominance was human blood type. This is the one that never sat right with me, and has been at least partly a mystery to me up until tonight. It was very clear to me this was not the same thing as incomplete dominance, yet every other example of something people were calling co-dominant was indistinguishable to me from incomplete dominance besides minute differences in phenotypic expression (eg: roan cow making both red and white hairs instead of pink hairs).

I had all the pieces to this puzzle for a while, but finally connected them tonight. I was long convinced there was simply no way there was only one mutation responsible for 6 different possible genotypes in blood type, so I figured at the least there were two mutations responsible for it. Then tonight, it hit me. I was thinking about allelic mutations in bed after making a post in a thread here, and the following ideas came to me all at once. Blood type O is wild-type (which I had determined a while ago), and types A and B are allelic mutations. Their mode of inheritance is dominance (AO is phenotypically identical to AA), but neither is dominant over the other, so in an individual with blood type AB, both are expressed. I'm assuming the term co-dominant refers to how types A and B are both dominant to type O, but both are expressed when paired with each other. I was actually comparing blood type to super stripe ball pythons when I thought of this. It really is the only explanation I can come up with for the genetics of human blood types that makes any sense. Anyway, I don't know if someone has come up with the same explanation before, because I've been pondering this for a very long time, and have asked multiple individuals and gotten no real explanation of what exactly the difference between co-dominance and incomplete dominance is until now. (I'm not even sure that was meant to be the difference when the term was coined - I've just assigned it to type AB blood in my mind since the term incomplete dominance described any other mutation in which the heterozygous phenotype was different from the wild-type as well as different from the homozygous mutant phenotype. By the way, I don't like the term co-dominance anymore now than I did when I first heard it. To me it still doesn't describe a different form of inheritance of a phenotype.)

If I'm wrong on this, and there's a geneticist around who knows better, I would love to be corrected - I always love a good talk about genetics - but like I've said this is the only explanation I have for human blood type. I made the comparison when I realized that AB can't reproduce itself when bred to OO (wild-type), but will only make AO and BO offspring. This is the same way that when a super stripe is bred to a normal, all you will get are spectre and yellowbelly offspring (the only difference being that yellowbelly and spectre are both examples of incomplete dominance).

Anyway, now that this is off my chest, hopefully I'll be able to shut my mind off long enough to get some sleep considering I have to be up in five hours, though I find the prospect unlikely.

[Big Gunns]

Do you think you can have a shorter one so BG can comment on it?

[BOWSER11788]

i thought Bg could read at lighting fast speed, lol

[Jamielvsaustin]

Now in english...please.

What's the difference between co dominance and incomplete dominance? Or what do "they" say is the difference? And what do you think it is?

Is that your delima? That you don't think there is such thing as incomplete dominance?

Seriously, can you break it down for me? I am interested, just not smart enough to follow along

[Russ Lawson]

Now in english...please.

What's the difference between co dominance and incomplete dominance? Or what do "they" say is the difference? And what do you think it is?

Is that your delima? That you don't think there is such thing as incomplete dominance?

Seriously, can you break it down for me? I am interested, just not smart enough to follow along

It's the other way around. I don't believe co-dominance is a form of inheritance (at least not in the sense that dominance, recessiveness, or incomplete dominance are). Most people working with ball pythons are aware that the mutations they are calling co-dominant are actually incompletely dominant.

It appears to me that the only textbook example I've been shown of co-dominance that differed in any way from incomplete dominance (being blood type) is actually the result of two dominant mutant alleles at the same locus. I believe the AB heterozygous individual is technically the only thing that can be correctly called co-dominant if anything in the mix was to be because both the A and B phenotype are equally expressed.

Just compare it to making a mojave x lesser BEL. Say mojave is AO and lesser is BO (O = wild-type). AB is a mojave x lesser BEL - when bred to a normal, all you get is AO and BO. In the case of human blood type though, AA and AO (or BB and BO) are phenotypically identical, unlike in the BEL complex.

This is my theory at least for now. Hopefully I've expressed it to you in a way that you can understand this time around. Maybe this explanation will be compressed enough for BG to come back and comment on as well.

[dc4teg]

One question, how is this an epiphany.... lol


I thought epiphany's were a major change in life

[Russ Lawson]

According to Wikipedia...

epiphany - the sudden realization or comprehension of the essence or meaning of something

Even so, I think about genetics pretty constantly, so this is somewhat major for me. I finally have an explanation for the one thing that I've come across in the subject that never made sense to me before.

[dr del]

Hi,

e·piph·a·ny (-pf-n)
n. pl. e·piph·a·nies
1. Epiphany
a. A Christian feast celebrating the manifestation of the divine nature of Jesus to the Gentiles as represented by the Magi.
b. January 6, on which this feast is traditionally observed.
2. A revelatory manifestation of a divine being.
3.
a. A sudden manifestation of the essence or meaning of something.
b. A comprehension or perception of reality by means of a sudden intuitive realization: "I experienced an epiphany, a spiritual flash that would change the way I viewed myself" (Frank Maier).

**edit**

Old fumble fingers beaten to it again egad!!

**end edit**


dr del

[dc4teg]

okay I guess I was wrong

[unspecified42]

It appears to me that the only textbook example I've been shown of co-dominance that differed in any way from incomplete dominance (being blood type) is actually the result of two dominant mutant alleles at the same locus. I believe the AB heterozygous individual is technically the only thing that can be correctly called co-dominant if anything in the mix was to be because both the A and B phenotype are equally expressed.

Just compare it to making a mojave x lesser BEL. Say mojave is AO and lesser is BO (O = wild-type). AB is a mojave x lesser BEL - when bred to a normal, all you get is AO and BO. In the case of human blood type though, AA and AO (or BB and BO) are phenotypically identical, unlike in the BEL complex.

The reason that it appears this way is not because it is true, but because of the nature of blood typing.

When we talk about 'A,' 'B,' 'AB,' and 'O,' we are talking about specific markers on the surface of the cell. 'O' is the absence of markers. That is why, phenotypically, 'AA' and 'AO' are the same thing- you gain nothing from the O. Both are being expressed equally, but you just can't see the 'O' being expressed.

Also, a roan cow (or horse or whatever) is not the same as incomplete dominance. You are thinking of the animal as a whole, not the individual hairs. Take a strawberry roan- they have both red and white hairs. Some hairs are red, some are white. If this color trait were incompletely dominant instead of codominant, you would have an animal with hairs that were all one color, and that color would be an intermediate between the two- so a lighter shade of red.

Think of it as flowers. If you take a white flower and crossbreed to a red one, a plant with incomplete dominance for the color gene will produce a pink flower. A plant that has a codominant color gene will produce a flower with some white petals and some red petals.