Beyond Fifty Shades: The Genetics of Horse Colors

Abstract

Since the dawn of horse domestication, coat colors have always fascinated humankind. In the last century, knowledge of genetics and development of scientific tools have become powerful enough so that the effects of many DNA mutations could be critically studied. Coat color nomenclature varies according to countries and breed associations; in addition, many factors can modify the color of the coat, such as sun exposure, age, sex, and nutritional status of the animal. Nevertheless, horses are capable of producing only two pigments. Several genes have been indicated as putative to coat color modification, altering the basic color by dilution, redistribution, or lacking of pigments.

Coat Color Roan Shows Association with KIT Variants and No Evidence of Lethality in Icelandic Horses

“…A particular difficulty when dealing with roan is the indubitable identification: roan could easily be confused with gray [ 20 ]. Additionally, similar color patterns, with white hair intermingling with colored hair, exist, e.g., rabicano or roaning/roaned [ 15 ], vanish roan caused by the leopard complex [ 21 , 22 ], Sabino [ 23 ] and other KIT- mutations [ 9 ], even though most of them have not been reported in the Icelandic breed so far. It is quite challenging to identify a roan foal correctly, as their white undercoat is mostly invisible in the foal coat until their first shedding.…”

Synergy betweenMC1RandASIPfor coat color in horses (Equus caballus)1

“…Horse coat colors were classified according to previous studies (Rieder, 2009;Neves et al, 2017;Sponenberg and Bellone, 2017;Figure 1a). Briefly, gray horses are born with an original coat color (such as black, bay, or chestnut) but gradually loose hair pigmentation at ages (6 to 8 yr) but maintained the dark skin.…”

“…MC1R protein located on the surface of melanocytes and activated by melanocyte stimulating hormone (MSH) leading to the production of eumelanin, which is the wild-type allele E E (Chen et al, 2017). The MC1R C901T mutation generates a recessive allele (E e ) that leads to the production of only pheomelanin within melanocytes (Neves et al, 2017). The eumelanin is a black pigment, whereas pheomelanin is a red/yellow pigment (Jackson, 1994).…”

“…The eumelanin is a black pigment, whereas pheomelanin is a red/yellow pigment (Jackson, 1994). Melanocytes that are homozygous for the recessive mutation (E e E e ) at MC1R cannot be activated by MSH, leading to the production of only pheomelanin (Suzuki et al, 1996;Neves et al, 2017).…”

“…An 11-bp deletion mutation at base 192 in exon 2 of ASIP (allele A a ) lead to loss of agouti signaling protein function, yielding a black phenotypic in the horse (Rieder et al, 2001). Combination of specific genotypes at MC1R and ASIP result in three basic phenotypes: black (E E E − -A a A a ), bay (E E E − -A A A − ), and chestnut (E e E e -A A A − or E e E e -A a A a ) (Neves et al, 2017). The superscript dash character ( − ) in the E − and A − alleles means any genotype at that gene.…”