INTRODUCTION TO GENETICS
COMPARATIVE GENOMICS CENTRE

Mail Address: Comparative Genomics Centre,
Molecular Sciences Bldg 21, James Cook University,
Townsville, 4811, Queensland, Australia
Telephone: 61-7-4781 6265 Fax:  61-7-4781 6078


COAT COLOUR IN LABRADORS
     Only three coat colours are recognised in labradors: black, chocolate and yellow. Although slight variations in coat shading are conferred by a number of genes, distinction between these three main colour groups are encoded by only two loci.
     One of two alleles can be expressed at the E locus: E (big E) and e (little E). A single copy of the E allele prevents the expression of a yellow coat colour. Dogs that express one or two copies of the E allele at the E locus are black or brown; the E allele is dominant. Dogs that express two copies of the e allele at the E locus are yellow; the e allele is recessive.
    One of two alleles can be expressed at the B locus: B (big B) and b (little B). Providing a dog is not homozygous e at the E locus, dogs that express one or two copies of the B allele at the B locus are black; the B allele is dominant. Providing a dog is not homozygous e at the E locus, dogs that express two copies of the b allele at the B locus are chocolate; the b allele is recessive.
Image courtesy Wing-N-Wave Labradors


    The following table illustrates the possible combinations of alleles associated with each of the three coat colour phenotypes observed in labradors.
 
PHENOTYPE
E
B
Image courtesy Wing-N-Wave Labradors
e e
B B
or
B b
or
b b
Image courtesy Wing-N-Wave Labradors
e E
or
E E
B B
or
B b
Image courtesy Wing-N-Wave Labradors
e E
or
E E
b b

ASSIGNMENT:
What parental genotypes could produce a litter containing pups of all three coat colours?


A NOTE ON NOMENCLATURE:
    Gene names are italicised in order to distinguish them from any protein products that they may encode - the names of which are not italicised. Capitalisation of the first letter of an allele name is conventionally used to denote the dominant allele; lower case to denote a recessive allele.The allele expressed at a particular locus is indicated by following the gene name with the superscripted allele name (e.g. Ee). Heterozygosity can be indicated with a forward slash (/) between the two allele names (e.g. EE/e). Where a single functional allele dominates, it may be described as the "wild type" allele and be indicated with a plus symbol (+). Homozygosity for the wild type allele may therefore be indicated by +/+.


COAT COLOUR GENETICS LINKS: OTHER GENETICS LINKS: OTHER LINKS: Comparative Genomics Centre, James Cook University, Key words: Autoimmune diabetes, Type 1 diabetes mellitus, childhood diabetes, lupus, systemic lupus erythematosus, haemolytic anaemia, hemolytic anemia, Coombs' test, antinuclear antibodies, renal failure, glomerulonephritis, gastritis, type A gastritis, pernicious anemia.