HETEROZYGOTE DEFICIENCY CAUSED BY A NULL ALLELE AT THE BOVINE ARO23 MICROSATELLITE

Non-Mendelian inheritance and heterozygote deficiency were observed wi thin the International Bovine Reference Panel (IBRP) when genotyped fo r AGC trinucleotide microsatellite ARO23. Chi square analysis showed a significant difference between the observed and predicted heterozygos ity among 37 unrelated individuals. PCR reactions using an alternative primer designed to avoid a putative mismatch resulted in the appearan ce of an additional allele with a frequency of 0.30 and the restoratio n of Mendelian inheritance. Sequence analysis of this allele showed a cytosine insertion 2 bp from the 3' end of the original priming site c ausing the failure of allele amplification. The presence of a segregat ing null allele may be suspected when heterozygote deficiency is obser ved.