GENETIC POLYMORPHISM OF MILK PROTEINS IN GOATS
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Date
1996
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COLLEGE OF VETERINARY AND ANIMAL SCIENCES-MANNUTHY,THRISSUR
Abstract
The present investigation was undertaken to identify the
biochemical polymorphism at different milk protein loci and to
establish their inheritance pattern in Malabari and its exotic
cross viz., Alpine x Malabari. It was also envisaged to
analyse the association of different milk protein variants
with lactation milk yield. Hundred goats belonging to
Malabari (50) and Alpine x Malabari (50) were typed for milk
protein variants employing horizontal Polyacrylamide Gel
Electrophoresis (PAGE). The milk protein loci studied were
Alpha Si casein, Alpha Sj casein. Beta casein. Kappa casein and
Beta lactoglobulin.
Two Alpha Si casein variants, the faster Alpha Si casein
F and the slower Alpha Si casein S with three phenotypes Alpha
Si casein AA, Alpha Si casein AB, and Alpha Si casein BB were
observed. S allele had the frequency of 0.52 in Malabari and
0.70 in Alpine x Malabari crossbreds. The gene frequency of
Alpha Si casein F and Alpha Si casein S were 0.48 and 0.52 in
Malabari and 0.30 and 0.70 in Alpine x Malabari crossbreds,
respectively. The frequency of S allele was higher in both
the populations.
Alpha Sj casein locus exhibited three phenotypes viz., AA,
AB and BB controlled by two alleles A and B. A allele had the
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higher frequency of 0.71 in Alpine x Malabari crossbreds
compared to 0.62 in Malabari. Higher frequency of AA phenotype
was found in Alpine x Malabari (0.52) and that of AB phenotype
in Malabari (0.44) .
Two alleles namely A and B contributed three phenotypes
viz., AA, AB and BB at the beta casein locus in both the
populations studied. Malabari showed higher frequency of B
allele (0.55) while Alpine x Malabari had higher frequency of
A allele (0.60) . Beta casein AB phenotype had higher frequency
in Malabari breed (0.54) .
Kappa casein locus showed two alleles A and B contributing
three phenotypes viz. , AA, AB and BB. The frequency of A
allele was higher in both the population. The phenotype AA was
higher in Alpine x Malabari crossbreds (0.56) while Malabari
had higher frequency of AB phenotype (0.48)
Two alleles namely A and B with three phenotypes AA, AB
and BB were identified at Beta lactoglobulin locus. The
phenotype AA was dominant in Alpine x Malabari crossbreds
(0.50) and the frequency of BB phenotype was almost similar in
both Malabari and Alpine x Malabari crossbreds (0.14 in
Malabari and 0.12 in Alpine x Malabari crossbreds). The gene
frequency of Beta Ig A was found to be 0.65 in Malabari and
0.67 in Alpine x Malabari crossbreds.
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Both the populations studied were in genetic equilibrium
with respect to these five milk protein loci. No significant
diversity was found to exist between genetic groups.
The genetic variability in the populations was calculated
by estimating the heterozygosity. The overall heterozygosity in
different populations indicated that the Malabari breed had
comparatively higher degree of heterozygosity (0.4711) followed
by Alpine x Malabari crossbreds (0.4209) . In Malabari maximum
heterozygosity was observed at Alpha Si casein loci (0.4992).
In Alpine x Malabari maximum heterozygosity was observed at
Beta casein locus (0.4800) .
The study of association between the genes controlling
synthesis of milk proteins showed significant association
between the Beta casein with the Beta lactoglobulin BB types in
Alpine X Malabari crossbreds. All the other combinations of
genes did not show any significant association.
Milk protein variants were not found to be associated with
the lactational yield (120 days) of the goats.
The present study could establish the existence of
biochemical polymorphism at Alpha Si casein, Alpha Sj casein,
Beta casein. Kappa casein and Beta lactoglobulin loci in
Malabari and Alpine x Malabari crossbreds studied.
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