The major components of hair are keratins and keratin associated proteins (KRTAPs). KRTAPs form the interfilamentous matrix between intermediate filament bundles through extensive disulfide bond cross-linking with the numerous cysteine residues in hair keratins. A variable number of approximately100-180 genes compose the KRTAP gene family in mammals. KRTAP gene family members present a typical pattern of concerted evolution, and its evolutionary features are consistent with the evolution of mammalian hair. KRATP genes might be more important in determining the structure of cashmere fibers in domestic mammals like sheep and goats. KRTAP gene variants thus should provide information for improved wool by sheep and goat breeding.