The Agouti Locus, more commonly known as the A Locus, has three distinctly different genes, ‘A,’ ‘a(t),’ and ‘a,’ that control the placement of color on the hair shaft. The A Locus does not determine color, but instead dictates pattern.

Agouti ‘A’ Gene

  • Most dominant gene in the A Locus
  • Creates bands of color on the hair shaft and causes white circles around the eyes, bellies, ears, and under the tail. 
  • The agouti gene is completely dominant so it is notated as A_
  • Common colors caused by the Agouti gene are the chestnut agoutis, chinchilla variations, and steel. 

Tan ‘a(t)’ Gene

  • The tan gene is dominant over the ‘a’ gene but is recessive to the dominant ‘A’.
  • This gene creates gold or silver ticking over the original color. 
  • Common colors include Silver Marten and Black Otter.

Self ‘a’ Gene

  • The most recessive gene on the Agouti Locus, so when it is expressed, it is always going to be homozygous and will be notated as ‘aa.’ 
  • This gene removes bands of color on the hair shaft. 
  • Common colors are Chocolate, Black, and Blue.

To view a picture dictionary of the many colors affected by the Agouti Gene check out the Color Guide!

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