To determine the genetic variability and population structure of
the
β-lactoglobulin (LGB) locus in
the Argentinian Holstein breed, milk samples from 12 herds at
four locations in Córdoba, Argentina,
were analysed. Allelic and genotypic frequencies of LGB variants were compared
by contingency
tables. A G-test was applied to detect Hardy–Weinberg
equilibrium. LGB A allele frequency was 0·43
and B allele frequency was 0·57. Allelic and genotypic
frequencies indicated great homogeneity among
populations. Most of the populations were in Hardy–Weinberg
equilibrium. According to the
fixation index, populations were panmictics. The partition of the
F-statistic demonstrated that mating
was at random, although there was a slight excess of heterozygotes, and
there were no genetic
differences among populations. The Shannon–Weaver index
showed that more than 96% of the total
genetic diversity for this locus is attributable to the differences
within each herd. The diversity among
herds within locations and among locations accounted for <4% of
the total variation. Phenograms
obtained by the Nei procedure for genetic distances disclosed the
separation of the herds into two
groups, one with an average frequency of LGB B of 0·61 and the
other with an LGB B frequency
of 0·53. Locations defined two clusters, but the divergence
among populations was not important.
These results indicated that the Argentinian Holstein breed from
Córdoba constitutes one population.