Agouti coloration in guinea pigs vs. recessive black

Agouti coloration is one of the basic coat color types in guinea pigs and is characterized by the typical banding of individual hairs. Each hair contains alternating segments of dark and light pigment, which gives the coat a grainy appearance or the impression of a mixture of dark and light shades.

The development of this type of coloration is controlled by the ASIP gene, which encodes the agouti signaling protein that affects the activity of melanocytes—cells responsible for pigment production in the coat. Mammalian coat pigmentation is primarily based on two types of pigment: dark eumelanin (black or brown pigment) and light pheomelanin (yellow to red pigment). The ASIP protein acts as an antagonist of the MC1R receptor, which regulates the production of dark pigment. When the MC1R receptor is active, cells produce dark eumelanin. When its activity is temporarily blocked by the ASIP protein, lighter pheomelanin is produced.

The c.181_184delTTCA mutation in the ASIP gene leads to a loss of its function, meaning it is unable to block the MC1R receptor. In such a case, there is continuous production of dark pigment, resulting in a uniform black coat.

The mutation is inherited in an autosomal recessive manner. This means that individuals with a uniform black coat have inherited the mutated gene from both parents. Carriers of the mutation have a typical coloration but can pass the mutation on to their offspring. When two heterozygous individuals are bred, theoretically 25% of the offspring will be mutation-free, 50% will be carriers, and 25% will inherit the mutated gene from both parents.

A genetic test can clearly determine the genotype of an animal and provides valuable information, especially for breeding planning and for better understanding the genetic mechanisms influencing guinea pig coat coloration.

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Reference:

Lai, W., Hu, M., Zhu, W., Yu, F., Bai, C., Zhang, J., Yan, S. : A 4-bp deletion in the ASIP gene is associated with the recessive black coat colour in domestic guinea pigs (Cavia porcellus). Anim Genet 50:190-191, 2019. Pubmed reference: 30746725