Colour inheritance: the agouti locus - Page 1

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pod

by pod on 30 August 2011 - 08:08

It has been known for over a decade, from breeding data, that four alleles exist in the Agouti locus - Sable Ay, wolf sable aw, tanpoint at and recessive black a.  Now, at last, we have publication of the DNA evidence to support this!

There are many threads on this forum on this topic and I know it is a long held belief in the GSD community that the saddle as allele exists.  Now we have proof that it doesn't, and that all the variation in the distribution of eumelanin (black) and phaeomelanin (tan) pigment in saddle, black & tan, bicolour, blanket...... etc etc, is down to genes and modifyers distinct from the A locus.  All of these patterns are in fact tanpoint at.

This of course applies to all breeds with these coat patterns, not just the GSD.


"Agouti Signaling Protein (ASIP) controls the localized expression of red and black pigment in the domestic dog through interaction with other genes, such asMelanocortin 1 Receptor and Beta-Defensin 103. Specific ASIP alleles are necessary for many of the coat color patterns, such as black-and-tan and saddle tan. Mutations in 2 ASIP alleles, ay and 
pod

by pod on 30 August 2011 - 08:08


"Agouti Signaling Protein (ASIP) controls the localized expression of red and black pigment in the domestic dog through interaction with other genes, such asMelanocortin 1 Receptor and Beta-Defensin 103. Specific ASIP alleles are necessary for many of the coat color patterns, such as black-and-tan and saddle tan. Mutations in 2 ASIP alleles, ay and a, have previously bhttp://jhered.oxfordjournals.org/content/102/Suppl_1/S11.abstract

by Til on 30 August 2011 - 11:08

Thanks for the interesting link!

darylehret

by darylehret on 30 August 2011 - 14:08

Approximately half of all annotated canine genes contain SINE repeats, bimorphic SINE insertions which are the basis for countless examples of allele-specific transcription patterns providing variation in their expression.  This accounts for a broad diversity easily observed by the naked eye, and of course, revealed in studies of the canine genome.  In comparison, the human race is estimated to only possess 11% SINE's in its genome.

To begin with, it should be realized that there is no ay (golden sable) in the german shepherd breed.  Additionally, there ARE distinct agouti allele types that differentiate the black & tan pattern from the bicolor dog, which expresses it's dominance over the bicolor variant.

It also should not go unnoticed that there are different allele types of minor variation among the "distinguished" phenotypes, such as sables which carry the dark ventral stripe (expressed right from the agouti loci), from those which do not.  Additionally, there are different allele types between the variations seen in black & tan phenotypes.

Comparatively, each allele which is closest to it's wild-type original (wolf gray sable, not golden sable) is going to have dominant expression over the closely-similar alleles which have a greater number of SINE insertions (aka, retrotransposons), deletions, and so forth.  This does NOT, however, mean that the lighter coated black & tan phenotype that appears more similar to sable enjoys COMPLETE dominance in it's pairing with a recessive couterpart.

Wherever you want to "draw the line" between what is "black & tan" vs. what is "bicolor", black & tan wins out in expression of phenotype, EXACTLY as rules of the order of dominance have been established, proving that the bicolor dog is expressed from the agouti locus, and nowhere else.  It is not controlled by a modifier from another location, instead merely has MORE absent or transposed information from the original wild-type than does the black & tan dog.

It must be brought to our awareness, that not all alleles of a specific type are identical copies of one another.  These are not physical elements.  There will naturally be some miniscule differences among the different strains of various intermittently separated bloodlines.   There will nat  T


Fenrir

by Fenrir on 30 August 2011 - 18:08

This is so, so, so fascinating to me :) I LOVE, LOVE this stuff.

pod

by pod on 31 August 2011 - 10:08

Daryl, I do know how difficult it can be to let go of a long held belief.  The full text of the paper is now available, please read it.  Here are some further quotes - 
"Based on the discovery of the variable SINE in this study, which can be used to identify the at allele, all 4 of the alleles at ASIP can now be discriminated with DNA testing. The present data (Table 1) demonstrate that dogs with the saddle tan phenotype are at/at at 
pod

by pod on 31 August 2011 - 10:08

"cont -  are at/at at ASIP. The difference between the traditional black-and-tan pattern and the saddle tan pattern is likely caused by a modifier gene that allows for the expansion of the phaeomelanin points.
http://jhered.oxfordjournals.org/content/102/Suppl_1/S11.full

pod

by pod on 31 August 2011 - 10:08

"The characterization of the mutation responsible for the black-and-tan phenotype in dogs can lead to a better understanding of ASIP and how it interacts with MC1R and other modifier genes to produce the phenotypic variation in color seen in domestic dogs This research will continue with investigation of the SINE region of ASIP and its role in alternate transcript production. Exploration of potential modifier genes of ASIP may explain the variation seen within ASIP alleles, such as at/
pod

by pod on 31 August 2011 - 10:08

cont - " such as at/at saddle tan and the grizzle/domino phenotype in Afghan Hounds and Salukis that results from an interaction of MC1R and the at/a
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