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#110200 - 07/25/13 06:28 AM Re: Definitions(genetic load and others) [Re: Wieslaw]
Wieslaw Offline
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Hi guys, I need to clarify the notion of "incompletely dominant". I understand the meaning of the words, but when I read various threads, people use it in different contexts, so which one is actually correct?

As an example , in this thread

http://www.the-coop.org/forums/ubbthread...=true#Post20980

T. Adkerson used it in following fashion:

Originally Posted By: T.Adkerson
What you have is a bird that is heterozygous birchen and wild type ER/e+. Birchen is incomletely dominant to e+ so you had an e+ phenotype expression on the down and the adult plumage is expressed as birchen.


The situation implies, that the result of one and the same cross can give different results(one time birchen, another time chipmunk). It is not what other people describe as incomplete dominance. Is it used correctly here?

To add: the second description of the incompletely dominant was: two doses work stronger than one.

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#110202 - 07/25/13 08:28 AM Re: Definitions(genetic load and others) [Re: Wieslaw]
Bushman Offline
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I think you can correctly use the term either way. I think you can also use it to describe non-allelic genes resulting in a different phenotype than was expressed in either parent, e.g., a cushion comb resulting from the combined effects of P and R. Usually RR/PP is indistinguishable from Rr/Pp and other combinations.
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#110204 - 07/25/13 08:44 AM Re: Definitions(genetic load and others) [Re: Bushman]
Henk69 Offline
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Only the second one is correct.
And i.m.o. birchen is dominant in chick down.
The sometimes (not) expressing of a trait is called penetrance.

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#110207 - 07/25/13 11:48 AM Re: Definitions(genetic load and others) [Re: Henk69]
Bushman Offline
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So what would you call my example (two posts prior to this one)?
I consider R and P to be incompletely dominant to each other.
I consider R to be completely dominant to r (no P/p present) and I consider P to be incompletely dominant to p (no R/r present).
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#110208 - 07/25/13 12:06 PM Re: Definitions(genetic load and others) [Re: Bushman]
Hen-Gen Offline
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Incomplete epistasis.
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#110209 - 07/25/13 05:35 PM Re: Definitions(genetic load and others) [Re: Hen-Gen]
KazJaps Offline
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Incomplete dominant is in reference to intermediate expression of heterozygous alleles of the same locus.

So yes, R is completely dominant to r+, P is incompletely dominant to p+, but P is not incompletely dominant to either R or r+ (nor Dv, Dc, bd, etc) as they are on a different locus.

Cushion/Walnut comb is a polygenic trait, multiple mutations involved. Any incomplete dominance of R/R P/p+ is just expression of het. P with p+, nothing to do with R locus.

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#110211 - 07/26/13 10:01 AM Re: Definitions(genetic load and others) [Re: KazJaps]
Bushman Offline
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Thanks! My dictionary defines epistasis as, "the dominance of one nonallelic gene over another." So, unless it is necessary to be terribly precise, in everyday conversation the use of the word dominant, or incompletely dominant to describe the relationship of R and P, does not seem entirely out of place. Do I need a new dictionary?
According to the definition, epistasis infers an unspecified degree or level of dominance.


Edited by Bushman (07/26/13 11:36 AM)
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#110216 - 07/27/13 03:23 AM Re: Definitions(genetic load and others) [Re: Bushman]
KazJaps Offline
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That definition would quickly get confusing, as there is dominant epistatic inheritance and recessive epistatic inheritance.
E & Co - dominant example,
c & E (& many others) - recessive example.

ie, dominant/recessive epistasis depends on whether the epistatic gene is dominant or recessive in inheritance. And I suppose incomplete dominant epistasis could apply also (can't think of a good example at the moment, but I suppose E could be technically incompletely dominant). R is completely dominant to r+.

But once again, the dominant/recessive/incomplete dominant, etc inheritance modes with epistasis is in reference to alleles of the same locus, not in reference to the epistatic/hypostatic relationship of genes from different loci. That is why two different defining words "epistatic" - gene masks expression of a gene on another locus, "hypostatic" - gene expression masked by a gene from another locus. Eg, you don't say c is dominant to E, or that E is recessive to c. E is hypostatic to c/c (plumage colour only, not epidermal pigment).

Definition of Epistasis:
http://ghr.nlm.nih.gov/glossary=epistasis

Quote:
  • One gene interferes with or prevents the expression of another gene located at a different locus.
    Definition from: Human Genome Project.
  • Epistasis is a circumstance where the expression of one gene is affected by the expression of one or more independently inherited genes. For example, if the expression of gene #2 depends on the expression of gene #1, but gene #1 becomes inactive, then the expression of gene #2 will not occur. In this example, gene #1 is said to be epistatic to gene #2.
    Definition from: Talking Glossary of Genetic Terms, from the National Human Genome Research Institute.


Don't know if incomplete epistasis is an accepted scientific term, but in my mind it would mean to not completely mask the gene expression of an allele from another locus. Ie, different meaning to incomplete dominant epistasis.

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#110574 - 09/08/13 01:00 PM Re: Definitions(genetic load and others) [Re: KazJaps]
Wieslaw Offline
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New question

I have just read the abstract provided by Kazjaps in the sticky thread( on congenital loco) and I'm not sure how to translate the "loco" part. Is it supposed to be the synonim for "crazy" as some sources suggest? The gene is responsible for the lack of control of the neck muscles at hatch. Any other words suitable to replace it without changing the meaning?

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#110579 - 09/08/13 07:27 PM Re: Definitions(genetic load and others) [Re: Wieslaw]
KazJaps Offline
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Posts: 2792
Loc: Australia
From "Genetics of the Fowl" (Hutt, 1949, pages 232-233)

Quote:
Congenital Loco, lo
Description.
A common abnormality in chicks and one that is nearly always lethal within a week after hatching is that designated by Knowlton (1929) as congenital loco.

The Spanish word loco, meaning insane, has been used colloquially by cattlemen on the Western plains to describe the symptoms induced in cattle after they have eaten certain toxic plants of the genus Astragalus.

Its use for the complete inability to balance that characterizes these chicks is perhaps temporarily justified till further study reveals the anatomical basis for the abnormality. The affected chicks hatch normally but cannot stand more than a few seconds. The head is drawn back, and the beak points upward, usually on one side (Fig. 66). Finally the chick topples over backward and lies on its back or side till righted, when the whole performance is quickly repeated. The condition suggests some defect in the mechanism for balancing, but the anatomical basis is entirely unknown.


So that is why it was called loco.

In PB&G (p 262), they have the mutation under the heading:
Congenital Loco or Star-gazer

On page 263 they mention Ataxia in Delawares, & say that it is not clear whether the trait was the same as classical Congenital Loco. They also mention congenital loco (or star-gazer) in other species.
----------------
So, you could use "star-gazer" as a generic descriptive term (in reference to the twisting back of the head). Might need the help of a medical person to confirm whether "Ataxia" is an accurate use of this medical term for lo mutation.

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