SEQUENCE-ANALYSIS OF THE BETA-LACTOGLOBULIN LOCUS IN HOLSTEINS IDENTIFIES 2 NEW RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS

The polymerase chain reaction (PCR) was used to amplify and clone a re gion from the beta-lactoglobulin (beta-LG) locus that spanned exons IV and V (849 bp). The DNA was amplified from both AA and BE homozygous individuals and sequenced. Sequence analysis revealed that the interve ning intron was 673 bp and that three nucleotide substitutions differe ntiated the A and B forms of beta-LG. One of these substitutions was a ssociated with the amino acid substitution (aspartic acid or glycine i n the A and B variants, respectively), and the other two which were no t reported previously were present in the intron sequence. These nucle otide substitutions resulted in restriction fragment length polymorphi sms (RFLPs) that could be used to genotype individuals. The new restri ction sites in the intron would result in a more accurate genotyping o f the beta-LG gene. Animals with B genotype were positive for the pres ence of two HaeIII restriction endonuclease sites, and type A animals were negative. Animals could also be genotyped on the basis of a polym orphism at a NlaIV restriction site. Genotyping of a random sample of 129 cows and 99 bull calves in Quebec revealed a frequency of 0.66 for the B allele. A comparison between bulls in current use by the artifi cial insemination industry (n = 114) and from the earliest years of th e industry (n = 70) revealed frequencies of 0.58 and 0.56, respectivel y. Thus, it is unlikely that the sire selection program has affected t he allelic frequency.