THE CHOCOLATE GREAT DANE

By Jane Chopson

Revised September, 1992

The Chocolate Great Dane has been observed to exist for at least 25 years. These dogs are not from only strange "hodge-podge" breedings, but are often from well-known lines. There are instances of excellent and frequently used stud dogs producing these colors. Since all too often the Chocolate is blamed on mixed-color breeding, inbreeding, or inter-breed crosses, it seems appropriate to look into the genetics of this color for the correct explanation.

The chocolate or liver gene is found in quite a few breeds; e.g., the liver Dalmatian, chocolate Poodle, the Vizsla and the liver Shorthair, to name a few. All these breeds carry the genes, although the resulting shades of red or liver vary with the different breeds.

Alternate forms of a gene, which occupy the same site on a chromosome, are known as "alleles" and are said to be members of an allelic series. An animal possesses two genes in each allelic series, one on each member of a chromosome pair. These genes may be dominant or recessive. There are two genes in the B (liver, chocolate, brown) series. The dominant member, designated B, allows the expression of full pigmentation. The recessive gene, designated b, when it occurs in duplicate, changes black pigment to liver or chocolate. A dog may have three possible combinations of genes in the B series: either BB, Bb, or bb. He must always have two genes of this pair. If a dog has two genes which are the same (BB or bb) he is said to be pure (homozygous) for the trait. If he has two different genes (Bb) he is hybrid (heterozygous) for the trait. For a recessive gene to manifest itself, the animal must be pure for that recessive gene. Hence, if an animal is Bb, he will not be chocolate because to be a chocolate a dog must be bb. BB and Bb dogs appear to be the same outwardly. A true chocolate dog, bb, has chocolate nose and leather pigment. Hence, if a dog has a chocolate coat but a black nose, it cannot be a bb dog but must derive its color from other genes. For example, the extreme recessive in the E allelic series is e. Two of these genes acting on an otherwise black dog produce the Irish Setter. He cannot be a chocolate because he has a black nose. The only time a true chocolate could have other than a chocolate nose would be in the case of a chocolate harlequin where the nose might be pink. A chocolate nose might be further lightened by the presence of dilution genes (dd). As stated earlier, bb changes an otherwise black dog to chocolate, liver or reddish brown. "AsAs bb CC DD EE mm SS" would be an example of the genotype for such an animal. An otherwise normal masked fawn possessing two chocolate recessives would become "ayay bb CC DD EmEm mm SS" and would appear to be peach or apricot in color with a chocolate mask and nose leather. An otherwise normal brindle, "ayay bb CC DD Emebr mm SS", will have chocolate stripes on a lighter background and a chocolate mask and nose. If an otherwise blue dog is bb, his genetic formula becomes "AsAs bb CC dd EE mm SS" and he will be a dilute chocolate. Finally, a pure harlequin with bb would become "AsAs bb CC DD EE Mm ss" and he would be a chocolate spotted harlequin. It should be noted that there are many more possible gene combination which would produce chocolate dogs but all must possess "bb".

Since a dog may be an acceptable color and still carry a recessive for chocolate (Bb), it is possible for two non-chocolate dogs to produce chocolate offspring. Each parent contributes one gene in each series to each puppy. A chocolate puppy is produced when each parent carries a chocolate gene and contributes a chocolate gene to the same puppy. If a dog is Bb, there is a 50:50 chance that he will pass on the chocolate gene to a particular puppy. If a dog is bb, then there is 100 percent chance that he will pass on a chocolate gene to all of his puppies. If a dog is BB, he cannot pass on the gene since he does not possess one. Two non-chocolate dogs which are hybrids (Bb non-chocolates which carry a recessive chocolate gene) when mated could produce chocolate (bb) puppies.

POSSIBLE BREEDINGS AND EXPECTED OUTCOME

1`

Genotype

Phenotype

BB

Non-chocolate

X

X

BB

Non-chocolate

= 100% BB

= 100% non-chocolate

2

Genotype

Phenotype

BB

Non-chocolate

X

X

Bb

Non-chocolate

= 50% BB, 50% Bb

= 100% non-chocolate

3

Genotype

Phenotype

BB

Non-chocolate

X

X

bb

chocolate

= 100% Bb

= 100% non-chocolate

4

Genotype

Phenotype

Bb

Non-chocolate

X

X

Bb

Non-chocolate

= 25% BB, 50% Bb, 25% bb

= 75% non-chocolate,

25% chocolate (50% of the non chocolates are carriers)

5

Genotype

Phenotype

Bb

Non-chocolate

X

X

bb

chocolate

= 50% Bb, 50% bb

= 50% non-chocolate

50% chocolate

6

Genotype

Phenotype

bb

chocolate

X

X

bb

chocolate

= 100% bb

= 100% chocolate

The preceding percentages are based on a large number of breedings. Figures for single litters often vary from these percentages, but the larger the number of puppies being considered, the closer the results will approach these averages. The results of breeding numbers 1, 3 and 6 will not vary with the size of the sample nor will the phenotypic results of breeding 2. As can be seen above, chocolate puppies cannot be produced unless both parents carry the gene a chocolate cannot come from one side only.

If we want to determine whether or not a suspect dog carries a gene for chocolate, a test breeding to a chocolate or known carrier must be made. Any non-chocolate dog who has a chocolate parent or who has himself produced the color must be a carrier (Bb) and test breeding is not required. Every puppy from a litter in which a chocolate has occurred must be suspect for the gene. When test breeding a suspect dog to a chocolate, 50% chocolates are to be expected if the suspect dog is a carrier. This 50% expectancy is valid for large samples. Small samples will probably vary from this percentage.

If a suspect dog is bred to a chocolate (bb) and produces a litter of six non-chocolate puppies, then the odds are 1:64 that he is not a carrier. If a litter of ten non-chocolates result, the odds change to 1:1024.

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Copyright 1992, Jane Chopson. All rights reserved. Our thanks to the willingness to share this article for educational purposes.