# Co-dominante



## Big Uli (Jun 17, 2013)

I'm a little confused about co-dominance 
I'm familiar with genetic through the budgies though I feel snakes go much deeper. 
Cinnamon and Opaline for example are a Gene/mutation in birds that only carry on the X chromosone. That means females can not be split or het.
Only males that carry just the one gene can be split as all x chromosones need the gene to be visible males being XX and females being XY
Visible female* XcY* and males *XcXc* with split being *XcX* the c representing cinnamon

If you followed me so far and I really hope I did a good enough job explaining so you could, would cinnamon and opaline be classed as co-dominant as there are cinnamon and opaline dominant mutation is birds

Genetics. Interesting but viable to give you a major headache:lol2:

I'll add a couple of diagrams just to clarify things shortly.


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## Big Uli (Jun 17, 2013)

Right. 
Dominant pied cock to Normal hen pairing
Cock is visible cinnamon
This right away tells us all visibly cinnamon offspring are female. 
All males will be split
It is not possible for males to be normal ie. non split for cinnamon
Also this diagram is not representative for the male female ratio. it only shows the possibilities in a 25% split 
You will have pieds and normals. All cinnamons are female all not showing cinnamon will be male. It's impossible for the pair to produce non cinnamon females

P for pied
N for normal 
c for cinnamon


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## paulh (Sep 19, 2007)

Actually, budgie genetics is more complicated than snake genetics. Because nobody has found any sexlinked mutant genes in snakes (yet).

By the way, co-dominate is a very common mistake. The correct spelling is co-dominant. And the hyphen is optional, so I usually skip it.

I am weak on the genetics for budgerigars. I am relying on the Genetic Calculator 1.3 Budgerigars

That chart says that cinnamon and opaline are sexlinked recessive mutants. Sexlinked because they are located on the X sex chromosome and recessive because the appearance only shows up in males when two copies of the mutant gene are present in the gene pair. With sexlinkage, we use only the males (in birds and snakes) to determine whether a mutant gene is dominant, recessive or codominant to the wildtype (normal) gene. With autosomal mutant genes, both males and females can be used.

Codominance as used here is a catchall term for any mutant gene that does not better fit in Mendel's dominant and recessive categories. So someone might say incomplete dominant or partial dominant or semidominant or overdominant or any of a dozen other terms. All are specialized subdivisions of codominance. For a breeder's purposes, codominant is good enough. A biochemist might need several specialized terms.

Two genes (A and a) can be arranged in three gene pairs -- AA, Aa, and aa. If the three gene pairs produce two possible appearances, the mutant gene is either dominant or recessive to the normal gene. If there are three possible appearances (one for each gene pair) then the mutant gene is codominant to the normal gene.

A is the dominant mutant gene, and a is the wildtype (normal) gene:
AA produces the full mutant appearance.
Aa produces the full mutant appearance (same as the AA's appearance).
aa produces the wildtype (normal) appearance.

A is the wildtype (normal) gene, and a is the recessive mutant gene:
AA produces the wildtype appearance.
Aa produces the wildtype appearance (same as the AA's appearance).
aa produces the mutant appearance.

A is the codominant mutant gene, and a is the wildtype (normal) gene:
AA produces the full mutant appearance.
Aa produces an abnormal (mutant) appearance that is not the same as the AA appearance.
aa produces the wildtype (normal) appearance.

if using two mutant genes in a multiple allele situation, replace the wildtype gene in the above charts with the second mutant gene.

Once you can fill out a chart with the three possible gene pairs and their appearances, you can figure out the dominant/recessive/codominant classification.

Hope that helps.


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