The agouti gene signals the on-off creation of eumelanin a pigment produced in a cell called a melanocyte. Eumelanin is black-brown in color. When the agouti gene has not signalled the creation of eumelanin a pigment called phaeomelanin is produced in the melanocyte. Phaeomelanin is red-yellow in color. The melanocyte feeds the pigment into the hair follicle.
|Tabby cat hair strand showing banding of pigmentation|
The message (signal) to create these two different types of pigment is effected by the action of a protein molecule called the agouti peptide and a hormone called the Melanocyte Stimulating Hormone (MSH).
The tabby gene dictates how the hairs are positioned throughout the body so it dictates how the tabby pattern appears. It works in conjunction with the agouti gene to create the well known tabby cat of which there are three types: classic blotched, spotted and mackerel or striped.