Let’s learn about color genetics
I have spent over 20 years studying both human and dog genetics. Taking hundreds of hours of classes to understand the genes and how they interact.
I have done this so that I can carefully and intentionally plan my breeding outcomes and better the breed. It’s critical when working with a breeder that they understand genetics and colors.
Understanding the genetics involved in breeding unique color variations of Yorkshire Terriers is crucial, as is ensuring that the breeder is knowledgeable in this area. These distinct colors are essentially mutations of the standard Yorkshire Terrier coat, developed through selective breeding to bring out recessive genes that determine coloration. However, because certain coat textures are associated with these color mutations, breeding efforts must be meticulous to preserve the desired coat quality.
To provide a brief overview of the genetic factors at play, it's essential to understand that each dog inherits two genes from each locus, with multiple loci contributing to coat color. Dogs can inherit two identical genes (homozygous) or two different genes (heterozygous) at each locus. Typically, a heterozygous dog will exhibit the characteristics of the most dominant gene it carries. Occasionally, incomplete dominance may occur, resulting in a blend of traits from both dominant and recessive genes. For instance, a genotype of "Ayat" (one copy of sable, one copy of tan points) would produce a dog with more black hairs than a homozygous sable (AyAy).
It's also important to differentiate between two types of pigments: eumelanin, which affects the coat, nose, and eyes, and phaeomelanin, which solely impacts coat color (commonly referred to as "red"). The term "red" here refers to the genetic name rather than the physical color observed, encompassing variations such as red, tan, cream, fawn, and blonde. Each locus specified below indicates which type of pigment it influences. However, it's worth noting that not all loci have been fully mapped, indicating that canine genetics is still an evolving field of study.
I have done this so that I can carefully and intentionally plan my breeding outcomes and better the breed. It’s critical when working with a breeder that they understand genetics and colors.
Understanding the genetics involved in breeding unique color variations of Yorkshire Terriers is crucial, as is ensuring that the breeder is knowledgeable in this area. These distinct colors are essentially mutations of the standard Yorkshire Terrier coat, developed through selective breeding to bring out recessive genes that determine coloration. However, because certain coat textures are associated with these color mutations, breeding efforts must be meticulous to preserve the desired coat quality.
To provide a brief overview of the genetic factors at play, it's essential to understand that each dog inherits two genes from each locus, with multiple loci contributing to coat color. Dogs can inherit two identical genes (homozygous) or two different genes (heterozygous) at each locus. Typically, a heterozygous dog will exhibit the characteristics of the most dominant gene it carries. Occasionally, incomplete dominance may occur, resulting in a blend of traits from both dominant and recessive genes. For instance, a genotype of "Ayat" (one copy of sable, one copy of tan points) would produce a dog with more black hairs than a homozygous sable (AyAy).
It's also important to differentiate between two types of pigments: eumelanin, which affects the coat, nose, and eyes, and phaeomelanin, which solely impacts coat color (commonly referred to as "red"). The term "red" here refers to the genetic name rather than the physical color observed, encompassing variations such as red, tan, cream, fawn, and blonde. Each locus specified below indicates which type of pigment it influences. However, it's worth noting that not all loci have been fully mapped, indicating that canine genetics is still an evolving field of study.
A Locus
A locus, also known as the "agouti series," plays a significant role in determining the distribution of eumelanin and phaeomelanin in the coat:
- Ay: Represents the Sable coloration, characterized by red with or without black tipping. Sable is dominant and can turn blonde.
- as: Represents Saddle-marked, featuring red with black markings on the back, neck, and tail. It appears to be dominant over tan points but not over sable.
- at: Denotes Tan points, which include a black body with red on the muzzle, chest, eyebrows, legs, and vent. This gene is only dominant over recessive black.
- a: Signifies Recessive black, characterized by a solid black coat with no red whatsoever. This trait is quite rare in occurrence.
- Ay: Represents the Sable coloration, characterized by red with or without black tipping. Sable is dominant and can turn blonde.
- as: Represents Saddle-marked, featuring red with black markings on the back, neck, and tail. It appears to be dominant over tan points but not over sable.
- at: Denotes Tan points, which include a black body with red on the muzzle, chest, eyebrows, legs, and vent. This gene is only dominant over recessive black.
- a: Signifies Recessive black, characterized by a solid black coat with no red whatsoever. This trait is quite rare in occurrence.
B Locus
B locus, also referred to as the "liver series or chocolate," influences the color of eumelanin:
- B: Represents Normal pigment, where a dog with Bb or BB genotype produces normal black eumelanin.
- b: Stands for Liver/Chocolate pigment, indicating that a dog with a bb genotype produces brown eumelanin instead of black.
- B: Represents Normal pigment, where a dog with Bb or BB genotype produces normal black eumelanin.
- b: Stands for Liver/Chocolate pigment, indicating that a dog with a bb genotype produces brown eumelanin instead of black.
D Locus
D LOCUS (“dilution series”, affects intensity of eumelanin). Also known as the “dilute gene.”
– D: Normal pigment and rarely fades.
– d: Diluted pigment. When homozygous (dd), turns the black color to blue and tan color to gold.
– D: Normal pigment and rarely fades.
– d: Diluted pigment. When homozygous (dd), turns the black color to blue and tan color to gold.
E Locus
The E locus, known as the "extension series," influences the distribution of eumelanin in the coat:
- Em: Represents Masked coloration, characterized by black on the muzzle and ears, occasionally spreading to black tipping on the chest and/or back.
- E: Denotes Normal extension, indicating no restriction of pigment. Although typically written with a capital letter, it is actually recessive to Em.
- e: Signifies Recessive red (although doesn’t always appear red in color), featuring a solid red coat overall, except for white markings. Dogs with an ee genotype are unable to produce any eumelanin (black) in their coat, causing any black areas to appear red. However, this does not affect the eyes and nose, meaning a recessive red dog may still have a black nose. The distribution of colored hairs determined by the A locus is influenced by interactions with alleles at the E locus. Often dogs with “ee” or “e” carrier can and will produce blonde color.
- Em: Represents Masked coloration, characterized by black on the muzzle and ears, occasionally spreading to black tipping on the chest and/or back.
- E: Denotes Normal extension, indicating no restriction of pigment. Although typically written with a capital letter, it is actually recessive to Em.
- e: Signifies Recessive red (although doesn’t always appear red in color), featuring a solid red coat overall, except for white markings. Dogs with an ee genotype are unable to produce any eumelanin (black) in their coat, causing any black areas to appear red. However, this does not affect the eyes and nose, meaning a recessive red dog may still have a black nose. The distribution of colored hairs determined by the A locus is influenced by interactions with alleles at the E locus. Often dogs with “ee” or “e” carrier can and will produce blonde color.
K Locus
The K locus, also known as the "black series," influences eumelanin in the coat:
- K: Represents Black coloration, resulting in a solid black coat throughout. This allele overrides the effects of the A (agouti) series, meaning any genes on the A locus will not be expressed. Often appears as KB.
- kbr: Denotes Brindle pattern, featuring black stripes on a red base. kbr is dominant over k, so a dog only requires one kbr allele to display the brindle pattern (though it will be overridden by one K gene). Brindle dogs will express genes on their A locus, with the red parts of the coat showing the brindle pattern while the black areas remain unaffected.
- k: Indicates Non-solid black, where a kk genotype dog will express genes present on its A locus. Often appears as kyky.
- K: Represents Black coloration, resulting in a solid black coat throughout. This allele overrides the effects of the A (agouti) series, meaning any genes on the A locus will not be expressed. Often appears as KB.
- kbr: Denotes Brindle pattern, featuring black stripes on a red base. kbr is dominant over k, so a dog only requires one kbr allele to display the brindle pattern (though it will be overridden by one K gene). Brindle dogs will express genes on their A locus, with the red parts of the coat showing the brindle pattern while the black areas remain unaffected.
- k: Indicates Non-solid black, where a kk genotype dog will express genes present on its A locus. Often appears as kyky.
M Locus
The M locus, referred to as the "merle series," impacts the intensity of eumelanin:
- M: Represents Merle pattern, characterized by black patches on a grey base or dark brown patches on a tan chocolate coat. This pattern dilutes random sections of the coat to a lighter color while leaving patches of full pigment. It's important to note that only areas of eumelanin can exhibit the merle pattern, while phaeomelanin remains unaffected. Merle is not a carried gene and only expressed. Meaning the dog is either Merle or Not Merle. If a breeder says the dog “carries Merle” they are uneducated and don’t understand genetics.
It’s extremely important to note: Breeders should NEVER breed two Merle dogs together. This is called and can produce a double Merle. This is an extreme health risk in puppies inclusive of death at birth, under development, blindness, deaf, and severe organ issues. Albeit none of this may appear initially, puppies can develop these issues as they mature into adults. Often times, double Merle is seen with a Merle pattern and white spots. It’s critical that if the breeder has a double Merle litter that they be tested immediately.
- m: Signifies Non-merle, indicating the normal expression of eumelanin without the merle pattern.
- M: Represents Merle pattern, characterized by black patches on a grey base or dark brown patches on a tan chocolate coat. This pattern dilutes random sections of the coat to a lighter color while leaving patches of full pigment. It's important to note that only areas of eumelanin can exhibit the merle pattern, while phaeomelanin remains unaffected. Merle is not a carried gene and only expressed. Meaning the dog is either Merle or Not Merle. If a breeder says the dog “carries Merle” they are uneducated and don’t understand genetics.
It’s extremely important to note: Breeders should NEVER breed two Merle dogs together. This is called and can produce a double Merle. This is an extreme health risk in puppies inclusive of death at birth, under development, blindness, deaf, and severe organ issues. Albeit none of this may appear initially, puppies can develop these issues as they mature into adults. Often times, double Merle is seen with a Merle pattern and white spots. It’s critical that if the breeder has a double Merle litter that they be tested immediately.
- m: Signifies Non-merle, indicating the normal expression of eumelanin without the merle pattern.
S Locus
The S locus, known as the "spotting series," impacts the distribution of all pigment:
- S: Represents No white spotting, where the entire coat is pigmented without any white markings. Often seen as “SS”.
- sp: Denotes Piebald pattern, featuring over 50% white with large pigmented patches on a white base. These dogs are predominantly white with patches of color and can carry either sp/sp or sp/sw alleles. Often the “Parti” colors either carry sp or are sp/sp.
- sw: Represents Extreme white, characterized by a piebald pattern with a high percentage of white. The color is typically confined to the base of the tail and head, with the majority of the body being white. Dogs with this pattern have two copies of sw/sw, indicating its high recessiveness.
All white spotting genes are believed to exhibit incomplete dominance over one another. For instance, a dog with one gene for no white and one gene for piebald will display an intermediate amount of white.
- S: Represents No white spotting, where the entire coat is pigmented without any white markings. Often seen as “SS”.
- sp: Denotes Piebald pattern, featuring over 50% white with large pigmented patches on a white base. These dogs are predominantly white with patches of color and can carry either sp/sp or sp/sw alleles. Often the “Parti” colors either carry sp or are sp/sp.
- sw: Represents Extreme white, characterized by a piebald pattern with a high percentage of white. The color is typically confined to the base of the tail and head, with the majority of the body being white. Dogs with this pattern have two copies of sw/sw, indicating its high recessiveness.
All white spotting genes are believed to exhibit incomplete dominance over one another. For instance, a dog with one gene for no white and one gene for piebald will display an intermediate amount of white.