Heterozygote deficiency caused by a null allele at the bovine ARO23 microsatellite

Non-Mendelian inheritance and heterozygote deficiency were observed within the International Bovine Reference Panel (IBRP) when genotyped for AGC trinucleotide microsatellite ARO23. Chi square analysis showed a significant difference between the observed and predicted heterozygosity among 37 unrelated individuals. PCR reactions using an alternative primer designed to avoid a putative mismatch resulted in the appearance of an additional allele with a frequency of 0.30 and the restoration of Mendelian inheritance, Sequence analysis of this allele showed a cytosine insertion 2 bp from the 3′ end of the original priming site causing the failure of allele amplification. The presence of a segregating null allele may be suspected when heterozygote deficiency is observed.