The Genetics of Variant Red and Changeling Coat Colour Phenotypes in Holstein Cattle
Dreger, Dayna Lee
Although most Holstein cattle are either black with white spots or red with white spots, two new coat colour traits called Variant Red (VR) and changeling, have recently been recognized by Holstein Canada. Variant red cattle look the same as red and white Holsteins but VR appears to be inherited as a dominant trait. Changeling cattle are born red and turn black by adulthood. Candidate genes for changeling included melanocortin 1 receptor (MC1R), agouti signalling protein (ASIP), attractin (ATRN), and melatonin receptor 1A (MTNR1A). Candidate genes for variant red included these same genes and β-defensin300 (putative K locus). Polymerase chain reaction restriction fragment length polymorphisms (PCR-RFLP) and sequencing were used to genotype single nucleotide polymorphisms (SNPs), which were recently discovered in our lab, for use in determining co-segregation in appropriate families. Cosegregation analysis excluded MC1R, ASIP, ATRN, or MTNR1A for changeling and VR, assuming single gene inheritance. Microsatellites and SNPs were used to map VR to a region on BTA27 surrounding and including β-defensin300 (LOD = 3.255). Cattle β-defensin300 was characterized from genomic DNA and mRNA from skin and appears to be homologous to canine β-defensin103 which is involved in black/red coat colour differentiation in many dog breeds. Although no mutations were found in the coding sequence, several were found in the 5’, putative promoter region. No polymorphisms consistently and exclusively occurred in VR and not in changeling and/or black and white Holstein cattle. Common relatives occurred in the pedigrees of several variant red and changeling cattle. A hypothesis was developed which suggests that a common mutation is required for the occurrence of either phenotype. A dominant mutation in a second gene would be required for VR, potentially a promoter mutation in β-defensin300. Two recessive alleles at a yet unidentified second gene, potentially a promoter mutation in ASIP, would be required for the changeling phenotype to occur.
DegreeMaster of Science (M.Sc.)
DepartmentAnimal and Poultry Science
ProgramAnimal and Poultry Science
SupervisorSchmutz, Sheila M.
CommitteeScoles, Graham; Laarveld, Bernard; Buchanan, Fiona; Plante, Yves