Polymorphism of growth hormone gene in Malabari goats (Capra hircus)
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Date
2002
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Department of Animal Breeding and Genetics, College of Veterinary and Animal Sciences, Mannuthy
Abstract
Malabari goats are noted for their high milk yield and meat production
qualities. They represent a unique genetic resource by virtue of their
adaptability, resistance to many infectious diseases and prolificacy in the humid
tropics of Kerala. They also exhibit considerable variation in individual
performance in milk production, growth rate and fecundity.
The growth hormone (GB) gene is a potential target for studies of
molecular variation because of its possible direct or indirect effects upon
growth, lactation and mammary gland development in dairy animals. The
polymorphism in the third intron of GH gene was investigated by polymerase
chain reaction (peR) and restriction endonuclease digestion.
Genomic DNA was isolated from a random sample of 196 genetically
unrelated Malabari does in second lactation belonging to three different
population groups based on geographical locations. The mean yields of DNA
from 5 ml of whole blood extracted by phenol-chloroform was 231.097± 11.65
ug. The ratio of optical densities at 260 and 280 nm was above 1.7 indicating
good deproteinisation.
Oligonucleotide pnmers based on bovine sequences were used for
amplification ofGH gene in goats. The successful amplification of the expected
768 bp fragment indicated the suitability of bovine primers for goats and
conservation of DNA sequence in related species. The digestion of the
amplified product with MspI restriction enzyme revealed two alle\es viz., Mspi
(+) and MspI (-) with gene frequencies of 0.70 and 0.30, respectively. In the
Malabari goats tested in this study only (+1+) and (+1-) GHIMspI genotypes
were encountered where as none of the animal was of the (-1-) genotype. [t is
suspected that the MspI (-) allele in the homozygous condition might be lethal
or linked to a lethal gene. The population of the Malabari goats investigated in
the present study was not under Hardy-Weinberg equilibrium though it was a
large random mating one with no known mutation, or migration. Hence, it is
suspected that the selection process acting against the (-/-) genotype through
reduced viability or early embryonic death may be a possible reason for the
disagreement of the Hardy-Weinberg equilibrium in Malabari goats for this
locus. It was observed that the goat population was in genetic equilibrium with
respect to growth hormone locus in all population groups. The genetic
equilibrium might be indicative of the homogeneity of different population
groups though they differed significantly w.ith respect to morphological and
other phenotypic characters.
Studies on the association of GHIMspJ genotypes with growth and milk
traits in Malabari goats revealed the following results. The (+1-) genotype was
superior to (+1+) genotype with respect to milk protein percentage in
population-I, The (+1-) genotype was found to be associated with significantly
high milk SNF percentage in population II and pooled population. The
GHIMspI genotypes did not exhibit significant effect on body weight, body
measurements, peak milk yield, milk fat and the litter size. The different
population groups differed significantly with respect to body weight, body
measurements like length, heart girth and height at withers, peak milk yield and
I litter size. These results revealed the influence of management and other environmental effects on growth traits in Malabari goats. It is concluded that the typing of the MspI polymorphism using PeR-based procedure is a very
efficient way to identify the GH genotypes in Malabari goats.
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172004