Dominant

[Jeanne]

Ok, Can someone explain the difference between Co-Dominant and Dominant?

I know the Mack Snows are Co-Dominant. I was reading the Urban Gecko web site and they are saying that their Snows are dominant, and they told me that that is why they haven't seen a Super form yet.

So, what is the difference?

Thanks to all who reply!

 

[Milwaukee Reptiles]

I think the Wikipedia article explains it pretty well.
http://en.wikipedia.org/wiki/Incomplete_dominance

Simple dominance

Consider the simple example in peas of flower color, first studied by Gregor Mendel. The dominant allele is purple and the recessive allele is white. In a given individual, the two corresponding alleles of the chromosome pair fall into one of three patterns:

* both alleles purple
* both alleles white
* one allele purple and one allele white

If the two alleles are the same (homozygous), the trait they represent will be expressed. But if the individual carries one of each allele (heterozygous), only the dominant one will be expressed. The recessive allele will simply be suppressed.

Incomplete dominance

In incomplete dominance (sometimes called partial dominance), a heterozygous genotype creates an intermediate phenotype. In this case, both the dominant and recessive alleles are expressed, creating a blended or combined phenotype. A cross of two intermediate phenotypes can result in the reappearance of either the parent phenotypes or the blended phenotypes.

The classic example of this is the colours of carnations.
R R'
R RR RR'
R' RR' R'R'

R is the allele for red pigment. R' is the allele for no pigment.

Thus, RR offspring make a lot of red pigment and appear red. R'R' offspring make no red pigment and appear white. RR' and R'R offspring make a little bit of red pigment and therefore appear pink.
[edit]

Co-dominance

In co-dominance, neither phenotype is dominant. Instead, the individual expresses both phenotypes. The most important example is in Landsteiner blood types. The gene for blood types has three alleles: A, B, and i. i causes O type and is recessive to both A and B. When a person has both A and B, they have type AB blood.

Another example involves cattle. If a homozygous bull and homozygous cow mate (one being red and the other white), then the calves produced will be roan-colored, with a mix of red and white hairs.

Example Punnett square for a father with A and i, and a mother with B and i:
A i
B AB B
i A O

Amongst the very few co-dominant genetic diseases in humans, one relatively common one is A1AD, in which the genotypes Pi00, PiZ0, PiZZ, and PiSZ all have their more-or-less characteristic clinical representations.

Most molecular markers are considered to be co-dominant.

 

[chad e]

thats cool that you found definitions for all three!:main_thumbsup:

 

[TheHiddenGecko]

If it is dominant, what would happen if it is bred to a normal because both are dominant? Would they just blend together so to speak?

 

[Milwaukee Reptiles]

That would depend on if the visible animal is a het or not. In the case of dominant traits, both the het and the homogenous versions will appear identical. If the animal is het and bred to a normal, it's possible to get 50% hets/50% normal (remember hets will show the trait). If the animal is homogenous dominant, every offspring will be a het version, so they will all show the trait.

 

[Grinning Geckos]

If it is dominant, what would happen if it is bred to a normal because both are dominant? Would they just blend together so to speak?

This is where it does get confusing. The full correct term is autosomal dominate for a trait that is not "normal".

To give a non-leo example, I have a joint disorder that is inhereted by autosomal dominance. I have it, therefore, one of my parents MUST show the exact same trait (my mom), and one of her parents MUST show the exact same trait (probably her dad)...etc. Now that I'm pregnant, my child has a 50 - 50 chance on inhereting it as well; assuming that I'm only het - LOL. If I'm homozygous, which isn't possible as my Dad is normal and my Mom's Mom was most likely normal, my child would have 100% chance of having it, and the expression of the gene is exactly the same the het form. There is no inbetween - my child will either have the condition, or he/she won't. If my child doesn't have the condition, he/she will never be able to pass on the trait as they don't contain any genes for it.

To bring it back to leos, we'll pretend someone happens upon a melanistic gene and it's autosomal dominate. It would not be a normal trait, but due to the inheretence it will dominate the dominate form of a normal.
______________________________________________________
normal/wild type = dominate
"melanistic" (oh...someday!) = autosomal dominate
______________________________________________________

normal x any recessive = normal looking hets.

normal x normal = normal

"melanistic" het x normal = 1/2 "melanistic" visual hets, 1/2 normal

"melanistic" homo x normal = "melanistic" visual hets (aka, a black leo)

"melanistic" het x "melanistic" het = 3/4 "melanistic" visual 66% hets 1/4 normal
*This one is a little confusing...you'll get 3 of 4 (if the stats hold) black leos, but you can't tell which one is the homozygous form, making all 3 of them 66% hets.

"melanistic" homo x "melanistic" het = "melanistic" visuals 50% het
*Again, you can't tell who the het is, but they will ALL be black leos

"melanistic" homo x "melanistic" homo = "melanistic" homo


As you can see from the example given, it would actually be harder to tell which one is homozygous, as so many combinations give you hets that look exactly the same.

Whew...that was tough to explain! :main_yes: I hope I didn't loose you!

 

[Jeanne]

Ok, I am a genetic moron...LOL I am still a little confused. I am getting one of the Urban Snows, a Female. So, if I breed her to a Normal Male, I will get 50% snows and 50% Normals, right. And you are calling the 50% Snows "Visible Hets", if they are Hets, then there must be a Super form, but Urban is saying there isn't a Super form. Then, what are they Het for? They are already Snows, how can they be Het for themselves?

I am confused

 

[TheHiddenGecko]

...Whew...that was tough to explain! :main_yes: I hope I didn't loose you!

I think I got it now. Thanks Shanti.

 

[Gregg M]

And you are calling the 50% Snows "Visible Hets", if they are Hets, then there must be a Super form, but Urban is saying there isn't a Super form. Then, what are they Het for? They are already Snows, how can they be Het for themselves?

There is really no "visible het" anything.... Co-dom snows are not really het for super snow..... That is just an easy way to explain incomplete or co-dom genetics....
When it comes to a dominant gene, there are no hets at all.... That would be like calling a normal leo a visual het for normal.... The normal spotted version of the leopard gecko is the dominant form.... This is what makes me think that the Urban snows may not be a true dominant.... If it were a dominant gene, when bred with a normal, all offspring would be a combo of normal and snow not 50% normal and 50% snow.... I think there is something else going on all together.... Might be co-dominant.... Co-dominant genetics do not necessarily have to result in a "super form".... The same is especially true for incomplete dominance....

 

[Jeanne]

There is really no "visible het" anything.... Co-dom snows are not really het for super snow..... That is just an easy way to explain incomplete or co-dom genetics....
When it comes to a dominant gene, there are no hets at all.... That would be like calling a normal leo a visual het for normal.... The normal spotted version of the leopard gecko is the dominant form.... This is what makes me think that the Urban snows may not be a true dominant.... If it were a dominant gene, when bred with a normal, all offspring would be a combo of normal and snow not 50% normal and 50% snow.... I think there is something else going on all together.... Might be co-dominant.... Co-dominant genetics do not necessarily have to result in a "super form".... The same is especially true for incomplete dominance....

Thanks Gregg!