The "amber" trait in cats, specifically Norwegian Forest Cats, is a unique coloration caused by a mutation in the MC1R gene, also known as the extension gene (E locus).
Definition
Amber is a yellow coat color identified exclusively in Norwegian Forest Cats. This color can vary from birth to adulthood, starting with a brindle brown coloration and transforming into an apricot or cinnamon shade in adulthood. This coloration is caused by a mutation in the MC1R (melanocortin 1 receptor) protein, which regulates the amount of eumelanin (dark pigment) and pheomelanin (light pigment). Activation of MC1R leads to the formation of dark coat, while inactivation of MC1R results in a lighter coat.
Genetic basis
The e allele is responsible for the amber coat in the Norwegian Forest cat and is due to a c.250G>A substitution in the MC1R gene. This variant follows an autosomal recessive mode of inheritance, which means that two copies of the variant are required to express this coat coloration. The presence of a single copy does not produce the amber phenotype, but it can be transmitted to offspring with a 50% probability.
Other relevant information
Cats with solid amber coats have dark nose and footpads, unlike amber tabby cats, which are born with pink nose and footpads, which darken over time.
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