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Coat color in mammals holds a particular fascination for all of us. The most important pigment responsible for coat color in mammals is called melanin, and mammalian coat color is almost entirely dependent on the presence (or absence) of the pigment melanin in the skin and hair. In mammals, melanin exists in two distinct forms: eumelanin, which is responsible for dark brown or black colors, and phaeomelanin, which forms yellow or reddish colors.

In order to understand how different coat colors arise in mammals, we must first study the cellular source of melanin, the melanocyte. In mammals, the melanocyte forms melanin pigment granules, which it secretes into surrounding cells. This process is the basis of mammalian hair, skin and eye color. The melanocytes responsible for hair pigmentation reside in the bulb of the hair follicle.

As you can see in this animation, eumelanin is produced when melanocyte-stimulating hormone (MSH), which is secreted by the intermediate lobe of the pituitary gland, binds with its receptor on the melanocyte. This allows the melanocyte to produce eumelanin pigment granules, which distribute themselves in the hair.

Even when eumelanin is produced, a range of different colors can be produced. The genetic basis for these colors is discussed in the next section.