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I'm hoping that someone here knows the color genetics well and can answer this question. Mostly to satisfy my curiosity.
I Adopted two GSDs out of a shelter. They came in as a bonded pair, seized from their owner for neglect. They were full grown (but underweight) but not much older than that. Probably about 1 year old. They do things that make me think they probably were siblings- sleep piled on top of each other like puppies, very similar personalities and mannerisms, very close to same size (the male is about 5# heavier than the female). But then again, this could all be due to same breed, being put together young with very little human interaction, etc.
The male is white. We've had white GSDs before, and his appearance is pretty typical. The female is jet black when you first look at her. Her undercoat is grey. She has a white patch on her chest and some white hairs on the underside of her tail and in the "armpits" of all 4 legs. She also has some white under the chin, and some random white hairs on her face. Her skin almost black in some places (like her ears), and her mouth skin is more purplish than the usual pink.
From what I can tell, black is recessive and so is white, but they're on different genes. So it seems like if I'm interpreting it correctly, they could be siblings, but it would be a pretty weird combination of not terribly common recessive genes. Can anyone provide additional insight?
 

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As I understand it, based on color genetics in the GSD they can be siblings.

In GSDs white is a recessive masking gene on the E locus. If a pup receives two copies of this gene (e), one from each parent, it will always be white, masking any other color s/he has from a different locus. So one parent could have been white (ee) but not both parents. Or neither parent could have been white but both must have carried one copy of the white gene (e).

Black is on the A locus and in the GSD it is recessive, meaning that both parents need to carry at least one copy of (a) for a pup to have a black coat. One parent could have been solid black (aa) if s/he carried only one (e), or have a white coat if s/he had two copies (ee). Or neither parent could have been black but both non-black parents must have carried one copy of a. For the pup to have a black coat, s/he needs to receive one a from each parent to be (aa), and have no or only one copy of (e).

Both recessives are common with different frequencies in different populations of GSDs. In AKC white GSDs and their puppies can be registered, so (e) is far more common among North American GSDs than those registered with the SV system which started excluding white decades ago. And of course it is ubiquitous in white GSDs bred for the color. Black a is very common in working lines, pet lines, and AKC lines, but has been pushed out in German show lines as they are bred for the red and black saddle pattern.

Color gene experts, please correct if I got this wrong!
 

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Yes, they can be siblings.

Don't worry about pictures as due to the fact that they're both GSD, they will have similar features. There isn't a person on here that can look at two random dogs and figure out if they're related or not.

If someone has grown up with the dogs, or has seen them on a weekly basis, then they'll notice certain familiar traits between siblings and probably even parents. But otherwise, no one can look at the conformation of two dogs and tell you they're siblings.
 

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White is a spotting gene in german shepherds. Meaning, every single white german shepherd is actually a black and tan, bicolor, sable, or pure black german shepherd that just happens to have a giant white spot over it's body.

So yes they could definitely be siblings. Your white german shepherd may very well be a black dog
 

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^ You're probably thinking of the Irish Spotting Gene - Different from the White Masking Gene. The Irish Spotting gene shows up in various colors, and is the cause of the sometimes white spot on a GSD's chest or white toes or feet.

Then the there is the White Masking Gene that makes a GSD all white, masks whatever colour genes the dog has, including Irish Spotting Gene. Wonder if that would make for a Double White dog! LOL!
 

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As Lucia said, the white color in GSDs is not due to the spotting gene on locus S. This is fortunate as at the spotting locus S the allele "extreme white" can occur (among other alleles such as "piebald"). "Extreme white" is associated with deafness. Since the white color is due to alleles not on the S but on the E locus, deafness is not an issue in white GSDs as it can be e.g. in white boxers.
 

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Discussion Starter #9
Thanks for the responses! This is pretty much what I thought, but it's nice to have it confirmed by those more in the know.

Does anyone know if there are genetic testing companies that will run a test for these various color genes? I could see breeders wanting to know. Based on all the recessives, if they are siblings, the black one would have a more than 50% chance of carrying one white gene, and the white one would also have a greater than 50% chance of carrying one black gene. It probably wouldn't be definitive, but could support likely vs unlikely.

So is the white spot on the black one's chest a separate spotting gene? These two have a lot going on.
 

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Thanks for the link. It never occurred to me that someone might want to test family relationships so I didn't realize it would be commercialized. $38 per dog seems pretty reasonable.
 

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You can also consider that they can be littermates from the same bitch and be sired by different fathers.
 

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So is the white spot on the black one's chest a separate spotting gene? These two have a lot going on.
Not the spotting gene, it's not present in GSDs. The white mark on the chest is 'residual white' when the black pigment doesn't fully spread during embryonic development. You see it quite often in GSDs. My own bicolor has a bit of white on her chest, too. Sometimes there is a pup with white toes on one paw, too. Or a bit of white on the underside of the tip of the tail. Once I saw an entire white tail tip in a sable GSD.

This page is a great resource for color genetics. Scroll down to 'residual white':
Dog Coat Colour Genetics
 
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