Sequence analysis of the beta-lactoglobulin locus in Holsteins identifies two new restriction fragment length polymorphisms
1996
Zhou, J.F. | Zadworny, D. | Kuhnlein, U.
The polymerase chain reaction (PCR) was used to amplify and clone a region from the beta-lactoglobulin (beta-LG) locus that spanned exons IV and V (849 bp). The DNA was amplified from both AA and BB homozygous individuals and sequenced. Sequence analysis revealed that the intervening intron was 673 bp and that three nucleotide substitutions differentiated the A and B forms of beta-LG. One of these substitutions was associated with the amino acid substitution (aspartic acid or glycine in the A and B variants, respectively), and the other two which were not reported previously were present in the intron sequence. These nucleotide substitutions resulted in restriction fragment length polymorphisms (RFLPs) that could be used to genotype individuals. The new restriction sites in the intron would result in a more accurate genotyping of the beta-LG gene. Animals with B genotype were positive for the presence of two HaeIII restriction endonuclease sites, and type A animals were negative. Animals could also be genotyped on the basis of a polymorphism 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 artificial insemination industry (n = 114) and from the earliest years of the industry (n = 70) revealed frequencies of 0.58 and 0.56, respectively. Thus, it is unlikely that the sire selection program has affected the allelic frequency.
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