How is the albino trait inherited in Dobermans?
Breeding studies, as well as nearly 30 years' worth of litters produced by private breeders, have established the pattern of inheritance of the albino trait in Dobermans. To understand this issue, let's take a look at Doberman color inheritance in general. In the United States, there are four accepted colors in the Doberman breed. These are black, red (also referred to as brown), blue, and fawn (also referred to as Isabella). In the Doberman breed there are only two sets of genes which interact to produce these colors -- the "B" series, and the "D" series. Each of these gene "series" contains two alleles (variants) in the Doberman breed; the "dominant" allele is referred to with a capital letter, while the "recessive" allele is referred to with a lower-case letter. Dominant alleles always "dominate", or hide, the effects of recessive alleles in the same gene series. So we have B, b, D, and d. B produces black, b produces red (brown), D produces full pigment (non-dilute), and d produces dilute pigment. Now, each dog carries two copies of the B series of genes and two copies of the D series of genes, and the dominant allele will always cover the effect of the recessive allele. So a black dog can be either BB or Bb, but a red dog must be bb. Similarly, a dog with non-dilute pigment can be either DD or Dd, but a dog with dilute pigment must be dd. Blue dogs are the dilute form of black, and fawn dogs are the dilute form of red. So here's what we're left with --
Black dogs can be BBDD, BbDD, BBDd, or BbDd
Red dogs can be bbDD, or bbDd
Blue dogs can be BBdd or Bbdd
Fawn dogs can ONLY be bbdd
Now, what does this have to do with albinos? As reported in the September 1984 Pipeline (the official publication of the DPCA), an albino to fawn breeding (not sponsored by the DPCA) produced all black puppies. Remember, the fawn parent MUST be bbdd -- it has NO copies of the dominant black gene, and NO copies of the dominant non-dilute gene. Since the fawn dog produced black puppies, both the black gene and the non-dilute gene MUST have been contributed by the albino parent. In addition, other breedings have proved that an albino dog bred to any colored dog which does not carry the albino trait will produce all colored puppies. Therefore, the albino trait is not dominant to either the black or dilution traits. This means that a dog must carry two copies of the albino gene in order to hide the other color traits. These breedings prove that the albino trait is not in the same gene series as either the black trait or the dilution trait. The albino trait must therefore be inherited at a separate site. Further, the albino/fawn breeding also proves that the albino trait in Dobermans is "epistatic" -- which means that it covers or "masks" the effect of both the black and dilution traits when the dog has two copies of the albino gene. The albino involved in the albino/fawn breeding had both the dominant black and the dominant non-dilution trait, so it would have been a black dog if there had been no albino genes present. Since it did have two copies of the albino gene, both the black and non-dilution genes were "masked" or "hidden". That's why the albino gene is often referred to as a "masking gene". The albino series of genes is classically referred to as "C". Although we now know that defects in several different genes can produce albinism (for example, the most common type of human albinism in the world is caused by a mutation in the P gene), for our purposes here we will refer to the gene as "C" for simplicity's sake. Further breedings have proved that the albino variant in dobermans is inherited as a simple recessive trait. Therefore, all albino dogs must carry two copies of the recessive gene, cc in order to appear albinistic. Normally colored dogs can be either CC or Cc. Dogs who are Cc can be any of the accepted colors, and there is currently no test (except for test breedings) which will detect the albino gene being carried by these dogs. Therefore, beginning in 1996, all dogs who are descended from albinos carry special registration numbers -- "z" numbers -- to warn breeders that these dogs may be carrying the albinistic trait.
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