Results
The frequency of the B allele in the Large White and Yorkshire populations was determined to be 0.40 and 0.49, respectively (data not shown). In both populations the observed number of heterozygotes was higher than the expected number based on allele frequencies and Hardy-Weinberg equilibrium. This difference was significant (P < 0.001) only in the Large White population.
The ESR genotype effect was significant (P < 0.05) only in the BF analysis and was nominally significant (P < 0.10) in the IBW analysis. In the BF analysis, animals possessing at least one copy of the B allele had 0.061 ± 0.023 inches more backfat than homozygous A animals (P < 0.01, Table 1). An ESR genotype x sex interaction was also detected in this analysis as heterozygous gilts were leaner than homozygous A gilts. In the IBW analysis, heterozygous animals were 0.120 ± 0.053 lbs heavier at birth than were the average of the homozygous animals (P < 0.05, Table 1). There were no detectable ESR genotype effects for TN, WW, AGE, ADG, or LMA (P > 0.10).