Understanding B-Locus Coat Color Testing
Whether you call it brown, chocolate, liver, or sometimes red in certain breeds, B-Locus can be a confusing coat color test.
Not only are there multiple B-Locus mutations that can contribute to a brown coat color, but some mutations can also appear on the same gene copy, which adds to the confusion.
In this blog, we’ll cover some basic biology of B-Locus mutations and help clarify how they affect coat color.
Why B-Locus Is Unique
B-Locus is unique compared to other genetic tests we offer.
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Most other tests involve a single mutation that arose once in one dog and was passed down through breeding.
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B-Locus has different mutations, which likely occurred separately in different dogs over dog breeding history.
Some B-Locus mutations appear in many breeds, such as the:
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bc variant
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bd variant
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bs variant
Other mutations are breed-specific, such as:
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ba in Australian Shepherds
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be in Lancashire Heelers
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bh in Siberian Huskies
Some breeds have a separate mutation with its own name, like CO-Locus or the Cocoa Locus in French Bulldogs.
No matter the mutation, they all lead to a brown coat color and a brown nose.
How Recessive Mutations Affect Coat Color
Since B-Locus mutations are recessive, a dog must inherit two copies of any B-Locus mutation to express a brown coat.
So how can a dog have two or more mutations but still have a black coat?
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Sometimes multiple mutations are carried on the same gene copy.
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Currently, we cannot determine whether mutations are on the same or different gene copy.
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We can only detect that they are present and must assume they are on different gene copies by default.
We’ve even seen rare cases where a dog carries three B-Locus mutations.
The best way to differentiate whether mutations are on the same or different gene copies is by looking at the dog’s nose color:
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Brown nose: Mutations are on different gene copies.
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Black nose: Mutations are on the same gene copy, and the dog should be considered a carrier for breeding purposes.
The following diagram illustrates these two potential situations:
Why Understanding B-Locus Matters
Understanding the complexities of B-Locus coat color testing helps you interpret your genetic test results and make appropriate breeding decisions.
Keep in mind:
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Different companies may test for some B-Locus variants but not others.
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Coat color is influenced by other mutations in addition to B-Locus.
We will cover the basics of coat color genetics in a future blog post.
In the meantime, if you have questions, don’t hesitate to reach out. We can help you plan your next breeding to achieve the coat color you want.