White spotting: When there’s more than two alleles

 So far, we have discussed genes which have only two alleles. However, that is not always the case: there can be more than two alleles for a given gene. One example is the MITF gene, which is the major gene that controls white spotting in dogs. This protein is required for the migration and survival of melanocytes into the skin during development. If it is not functional, it impairs the ability of the skin to make pigment, thus “covering up” the effect of other color genes. There are thought to be at least four alleles that can contribute (Karlsson, 2007). Depending on which alleles are present in a dog, the amount of white can vary from none (a solid-colored dog) to mostly white (Table 2 and Figure 1).

Table 2: Combinations of different alleles for MITF result in different amounts of white present in the coat.

Alleles Amount of white
SS None (solid colored)
Ssi Small amounts of white possible on face, chest, feet, and tail tip
Ssp More than 50% solid colored, with white on the face, chest, feet, collar, underbelly, and tail tip
sisp Approximately even amounts of color and white
sise More than 50% white with irregular splashes of color
sese Mostly white with only minimal areas of color, perhaps on one or both ears, an eye patch, or a spot near the tail
Figure 1: These dogs have different combinations of alleles of the MITF gene. The first dog probably has the genotype“Ssp“; the dog in the center is likely  “SS”; the dog on the right is likely “sese“. (Credits: Funny black dog by X posid from Publicdomainpictures. A black and white dog by Petr Kratochvil from Free stock photos. White dog with black ears by RetyiRetyi from Pixabay.)


There is a similar white-spotting gene in domestic cats that leads to the bicolor coat pattern commonly called “tuxedo” (Figure 2).  However, the genetic causes of domestic cat coat patterns are not well understood and there is no consensus on which specific gene controls white spotting in cats. Some studies suggest that the gene responsible is the feline version of the KIT gene (Cooper, et al. 2006; Montague, et al. 2014), but further research on mammalian pigmentation is needed before a conclusion can be made (Mort, et al. 2016).

An image of the author's bicolored cat in an undignified pose that displays the white spotting on the underbelly, nose, and paws.
Figure 2: An image of the author’s bicolored cat in an undignified pose that displays the white spotting on the underbelly, nose, and paws.


Human Connection – Blood Type

Human blood type was discussed in the previous section. You may remember that there are three alleles for the ABO gene: A, B, and O. A and B are codominant, meaning that if both alleles are present, both will be seen in the phenotype. A person with type AB blood has one A allele and one B allele.

O is recessive to A and B. A person with the genotype AO will have Type A blood. A person with the genotype BO will have type B blood. Type O blood results from two O alleles.


Photo credit: Kalaiarasy, from Wikipedia.


Unless otherwise noted, text and images by Lisa Bartee (2016) and Catherine Creech (2023).

Karlsson EK, Baranowska I, Wade CM, Salmon Hillbertz NH, Zody MC, Anderson N, Biagi TM, Patterson N, Pielberg GR, Kulbokas EJ 3rd, Comstock KE, Keller ET, Mesirov JP, von Euler H, Kämpe O, Hedhammar A, Lander ES, Andersson G, Andersson L, Lindblad-Toh K. 2007. Efficient mapping of mendelian traits in dogs through genome-wide association. Nat Genet. 39(11):1321-8.

Montague MJ, Li G, Gandolfi B, Khan R, Aken BL, Searle SM, Minx P, Hillier LW, Koboldt DC, Davis BW, Driscoll CA, Barr CS, Blackistone K, Quilez J, Lorente-Galdos B, Marques-Bonet T, Alkan C, Thomas GW, Hahn MW, Menotti-Raymond M, O’Brien SJ, Wilson RK, Lyons LA, Murphy WJ, Warren WC. 2014. Comparative analysis of the domestic cat genome reveals genetic signatures underlying feline biology and domestication. Proc Natl Acad Sci USA. 111(48):17230-5.

Cooper MP, Fretwell N, Bailey SJ, Lyons LA. 2006. White spotting in the domestic cat (Felis catus) maps near KIT on feline chromosome B1. Anim Genet. 37(2):163-5.

Mort, R. L., Ross, R. J. H., Hainey, K. J., Harrison, O. J., Keighren, M. A., Landini, G., Baker, R. E., Painter, K. J., Jackson, I. J., & Yates, C. A. 2016. Reconciling diverse mammalian pigmentation patterns with a fundamental mathematical model. Nature Communications, 7(1), 10288.


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Principles of Biology Copyright © 2017 by Lisa Bartee, Walter Shriner, and Catherine Creech is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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