An MspI polymorphism at the bovine growth hormone (bGH) gene is linked to a locus affecting milk protein percentage

SSCP analysis of the bovine growth hormone (bGH) gene in Israel Holstein da iry cattle uncovered five intragenic haplotypes, denoted A to E. Of these, Haplotype E differed from the others at six fragments; one of which corresp onded to the polymorphic MspI site in intron III, at which haplotype E carr ied the disabled MspI (-) allele. haplotype E was observed in a single sire only, carrying haplotype A as the second bGH allele. In 523 daughters of t his sire genotyped for the MspI polymorphism, heterozygous (+/-) as compare d to homozygous (+/+) daughters, showed a significant increasing effect on protein percentage and kg protein per year; and a decreasing effect (P < 0. 10) on milk somatic cell counts (MSSC). None of the daughters were homozygo us (-/-), indicating that the frequency of this allele in the general popul ation was essentially zero. Calculated skewness (g(1)) values for the two d aughter groups differed significantly with (+/-) daughters showing negative skewness (in the direction of lower protein percentage), and (+/+) daughte rs positive skewness (in the direction of higher protein percentage). The d irection of skewness in each group is indicative of the presence of a QTL h aving an increasing effect on milk protein percentage in coupling linkage w ith the MspI (-) allele in this sire, but at some distance from it. Maximum likelihood estimates of the proportion of recombination (r) between the pu tative QTL and bGH, and the allele substitution effect at the QTL (d), were r=033, a=0.07% protein, with standard errors 0.058 and 0.009% protein, res pectively.