the Blackest Ones: on exploring the significance of Cemani mutations

[urjtobreed]

[COLOR=FF0000]Genetics 101[/COLOR]

I am going to present information with out being  technical. This is overly simplified but will get the point across..

There are two genes that are basically responsible for black bone trait.The Fm gene and the sex-linked dermal melanin gene. What I mean by black bone is black pigment found in the organs, connective tissues, skin and on the bones of chickens- this is also called hyper-pigmentation or fibromelanosis.

It has been posted that hyper-pigmented birds have an unusual arrangement of a chromosome that is associated with the trait. Birds like the Cemani and silkie have a section of DNA that is duplicated. It looks like this ( this is not exact but will do to explain the situation)

other DNA  [COLOR=FF0000][   DNA section one ][/COLOR][COLOR=DDA0DD][ DNA section 2][/COLOR] [      more DNA        ] [COLOR=FF0000][ DNA section one] [/COLOR][COLOR=DDA0DD][  DNA section 2 ][/COLOR]  other DNA


this is not found in other chickens ,  other chickens have other DNA [COLOR=FF0000][ DNA section one][/COLOR] [COLOR=DDA0DD][DNA section 2][/COLOR] other DNA


1. The Fm gene is found in the duplicated section one 

2. Silkies and Cemani can have up to 4  genes for Fm or fibromelanosis. Each gene is working to produce the black pigment found in the bird. Genes are normally found in pairs. So you would think the most Fm genes a bird could have would be two ( one pair). This is not the case. Instead of having two genes producing a product that causes black pigment the black bone has 4 genes producing a product  that causes even more black pigment.

3. Birds that are the darkest skin color will have 4  Fm genes; along with= males will have 2 dermal melanin genes and  females will have one dermal melanin gene 

 males will be Fm/Fm/Fm/Fm  id+/id+ and females will be Fm/Fm/Fm/Fm  id+/w

 a bird with 4 Fm will be darker than one with 3 Fm; 3 Fm darker than 2 Fm, and two Fm darker than one Fm

4. Feather color is controlled by other genes the Fm gene and id+ gene do not control feather color

5. Shank color is controlled by skin color, the sex linked dermal melanin gene and dermal melanin inhibitor gene, and the E locus gene ( like extended black, wheaten etc.) and a few other genes ( like sex linked barring)

6. A bird that inherits a dermal melanin inhibitor gene (id) will produce very little black pigment even if it has 4 Fm genes- a bird that should have black skin will have grayish to white skin

Remember the dermal melanin gene is sex linked.

dark black bone male x  wheaten marans = F1 chicks with two Fm genes but the male and female offspring will not be the same even though both have two Fm genes

The males inherited one dermal melanin inhibitor gene  from the mother and will have light skin. The males will pass on the dermal melanin inhibitor gene to his daughters and to his sons producing light skin offspring even if he is crossed with a very dark female.

The female offspring will inherit a dermal melanin gene from the father and have dark skin.

The F1 offspring, which have two Fm, may pass on [COLOR=FF0000]no Fm[/COLOR] or  may pass on [COLOR=FF0000]one[/COLOR] or they may pass on [COLOR=FF0000]two[/COLOR] Fm to their offspring. So, if you back cross an F1 dark skin female to the black bone father- ( please do not ask how I came up with the one Fm, it is complicated)

the back cross offspring (BC1) can contain 4 Fm   or   3 Fm   or   2Fm   which would exhibit varying shades of dark skin.

the sex linked dermal melanin inhibitor is not found in the father or mother so there will not be any BC1 that have light skin.

7. Each one of the Fm have a section of DNA that controls how each Fm produces a product. I said product because the Fm gene does not actually make the pigment. The Fm gene holds the recipe for making a protein- the protein then sets into motion the cell activities that eventually produce black pigment. Hypothetically,  it is possible that the controlling parts of DNA control differently; this could cause one chicken to be darker than another.  The research indicates that each gene has the controlling DNA but does not indicate if there are differences in how the genes are controlled. The research also indicated that there were differences in the composition of some of the DNA in the sections and the Fm genes. This difference could be in the controlling DNA and would effect how the Fm functions- the difference in the Fm genes could also cause differences in expression of black pigment.

Tim

That is a great visual explanation, however you are misunderstanding a subtle but very important detail. Fm is caused by extra copies of the EDN3 gene. It cannot be accurately stated that a chicken can have up to 4 Fm genes. All chickens have 2 copies of the EDN3 gene as part of there normal genetic toolkit. These 2 copies are essential to normal melanocyte (pigment cell progenator) proliferation and migration and do not result in Fm on there own. It would be incorrect to say that EDN3 is the Fm gene. Fm only occurs when a chicken has 1 or 2 EXTRA copies of the EDN3 gene, resulting in roughly 50% or 100% over expression respectively (150% and 200% of normal). It is only when EDN3 is over expressed that it results in Fm. Therefore the normal 2 copies of EDN3 are ignored, they are a "given". The Fm "gene" is really the extra copies of EDN3.

So a chicken can only have 1 or 2 Fm "genes". Unless EDN3 were to be copied another time. CNVs are very rare so this is extremely unlikely and would likely result in a puddle of extremely black goo, sucking in all light and matter around it's immediate vicinity. Calamity ensues:
"Hey hon, do you you know what happened to the incubator? I had some super special eggs that were due to hatch. Oh-****!, what made that big hole!"

 

[Dipsy Doodle Doo]

What do EDN3 and CNV stand for?

 

[tadkerson]

 

[nicalandia]

Quote:
Its Short for Endothelin-3 and Endothelins are endothelium derived vasoactive peptides

 

[urjtobreed]

What do EDN3 and CNV stand for?

EDN3 = endothelin 3
CNV = copy number variation

 

[nicalandia]

Quote:
by any chance you are an old member of the Classroom at the coop forums

 

[Dipsy Doodle Doo]

Thanks : )

 

[urjtobreed]

Tim-

I respectfully disagree with your interpretation.

Deleterious mutations in EDN3 result in not only pigment abnormalities but functional abnormalities such as deafness and other significant issues:
http://m.hmg.oxfordjournals.org/content/6/10/1613.long

EDN3 is an essential gene for normal function.

Only 1 or 2 extra copies of EDN3 in addition to the normal 2 will make Fm, which is what I think you reiterated, but are interpreting it differently than I am.
Stating that Fm fowl have 4 Fm genes, listed as Fm/Fm/Fm/Fm is not correct or useful in my opinion. EDN3 does not equate to "Fm gene". Using your 4 gene genetic notation would lead someone to believe that a chicken could carry 1 to 4 copies, which is not the case. Sticking to Fm/Fm (two copies) notation for the fibromelanosis trait reflects the realities of inheritance of the trait and would be the most useful for breeding.

I hope you are looking at this as a postive intellectual debate. I wouldn't want this to turn negative like I have seen many other threads go. That is why I usually don't bother posting on forums.

 

[urjtobreed]

Quote:
by any chance you are an old member of the Classroom at the coop forums

No, I am mostly a lurker.

 

[nicalandia]

Quote:
Tim just doesnt like intellectual debates, I got in trouble for doing just that not too long ago