Report: The K-Locus (Brindle) and Cardigan Nose Color in Clear Red Dogs
Jeff Welch and Vivian Moran (CWCCA Health Committee)
An extension of the nose color study involved looking for additional genetic markers which might be predictive of nose color in clear red Cardigans (eeRed). One marker chosen was brindle, located at the K-locus or Beta-Defensin 103 (Ciampolini et al, 2012). The current test for brindle is unable to distinguish between the brindle allele (Kbr) and dominant black (KB), but the absence of dominant black in Cardigans allows the brindle allele to be identified from dominant black/brindle test results (Candille et al. 2009). This simply means that in Cardigans the presence of dominant black is analogous to the presence of brindle. We tested or receivedtest results from 10 clear red Cardigans, 6 brindle Cardigans (positive controls) and 3 red Cardigans (negative controls) to help determine if the presence of brindle (Kbr) correlated with the nose color in clear red dogs.
|Dog #||Nose color||Coat color||Genotype|
|01||Brown||Clear red||Heterozygous for brindle (KB test)|
|02||Brown||Clear red||Heterozygous for brindle (KB test)|
|03||Black (FWA)||Clear red||Heterozygous for brindle (KB test)|
|04||Black (FWA)||Clear red||Heterozygous for brindle (KB test)|
|05||Black||Clear red||Heterozygous for brindle (KB test)|
|06||Black||Clear red||Heterozygous for brindle (KB test)|
|07||Black||Clear red||Heterozygous for brindle (KB test)|
|08||Black||Clear red||Heterozygous for brindle (KB test)|
|09||Black||Clear red||Heterozygous for brindle (KB test)|
|10||Black||Clear red||Clear for brindle (KB test)|
|11||Positive Controls (6 Brindle dogs)||All heterozygous for brindle (KB test)|
|12||Negative Controls (3 normal red dogs)||All clear for brindle (KB test)|
|13||(FWA=nose color was black as a puppy but faded with age)|
The one clear red dog (#10) who tested clear for brindle would be phenotypically red, while the other nine clear red dogs would be phenotypically brindle were it not for the eeRed genotype. As can be seen, nose color is variable among these nine dogs and so brindle does not appear to be predictive of the nose color. However, the controls indicate that the current test for dominant black will identify brindle in Cardigans and can be used to determine if a clear red dog carries the brindle gene. This test, if used in conjunction with testing for agouti (Dreger and Schmutz, 2011), should be able to determine if a clear red dog is a tricolor black, a brindle, or a typical red and to distinguish between black brindle and minimally pointed tricolor dogs.
A very interesting finding was that within the study group all brindle dogs tested as heterozygous for brindle and no homozygous animals were found. While the study group was relatively small (6 brindle Cardigans), this is in agreement with data from other laboratories where no homozygous brindles were present in over 250 brindle dogs examined (Candillie et al. 2009,Oguro-Okano et al. 2011,Ciampolini et al. 2013). The number of heterozygous brindle Cardigans increases significantly if the results from clear red dogs are included(total dogs 15) and again no dogs were found to be homozygous for brindle.