2 POLYMORPHIC MICROSATELLITES IN A CODING SEGMENT OF THE CANINE ANDROGEN RECEPTOR GENE

A 0.6-kb segment of exon 1 of the canine androgen receptor gene contai ns two polymorphic CAG tandem repeats which encode strings of glutamin e homopolymers. The number of CAGs in each tandem repeat was determine d by (1) polymerase chain reaction (PCR) amplification of a gene segme nt containing both repeats, (2) cleavage between repeats with restrict ion enzyme EcoO109I and (3) fractionation of the restriction fragments containing individual CAG repeats by denaturing polyacrylamide gel el ectrophoresis (PAGE). Individual genomic DNA samples from 80 unrelated dogs (53 males plus 27 females for a total of 107 X chromosomes) cont ained 10-12 CAGs in the 5' repeats and 10-13 CAGs in the 3' repeats. T hirteen distinct androgen receptor genotypes were identified. Eleven ( or 41%) of the 27 unrelated females were heterozygous in one or both r epeat regions, whereas all male samples produced single bands as expec ted for X chromosome markers. A total of seven distinct haplotypes con tributed to the 13 genotypes. The 'polymorphism information content' o r 'PIC' for this seven-allele X chromosome marker was 0.67.