Single nucleotide polymorphism in the insulin-like growth factor-1 gene and its effects on growth traits in Yankasa sheep

Abstract

A study was conducted to determine single nucleotide polymorphism of the IGF-1 gene and its effect on
some growth traits in Yankasa breed of Sheep. Random samples of 100 sheep (50 males and 50 females)
were selected for the molecular study and the phenotypic evaluation. Animals were measured for growth
traits namely: birth weight, average daily gain, weaning weight, weights at 6, 8 and 12 months, chest girth
and height at withers. Blood samples were collected from the animal’s neck region through the jugular
veins into 0.5ml EDTA vacutainer tubes and transferred to the laboratory for DNA extraction. Total DNA
extraction was made with ZR-96 Genomic DNA miniprep. Frequency of alleles were calculated according
to Hardy-Weinberg’s equation and also subjected to Chi-Square analysis to test for Mendelian inheritance
ratio for band. Genotypes, growth traits, sex and interaction were determined through statistical analysis.
Both genotypic and allelic calculated χ
2
values (9.07 and 16.94) for Mendelian inherited ratio were greater
than the tabulated values of 5.99 and 3.84 at 5% level of significance. All growth traits (birth weight,
weaning weight, average daily gain, weight at 6 months, weight at 12 months, height at withers and chest
girth) with the exception of body weight (Kg) at 8 months showed significant (P<0.05) variations. With the
exception of average daily gain (g/day), which was non-significant (P>0.05) across the sexes, all other
growth characteristics differed significantly (P<0.05) across sexes with the highest traits in the male
compared to the females. Observed trend showed significant (P<0.05) interactions among the measured
traits with the exception of average daily gain. Male Sheep with AA and AB genotype were similar in
performance across all traits (birth weight, average daily gain, weaning weight, weight at 6 months, weight
at 8 months, weight at 12 months and height at withers) with the exception of chest girth (cm). It can be
concluded that Yankasa sheep with AA genotype had significant higher propensity for growth than those
with genotype AB and BB.Yankasa sheep with AA genotype could be used for genetic improvement
programs targeted to growth traits in Nigeria. It is recommended that polymorphism of the IGF-I gene may
be a potential molecular marker for growth traits in Yankasa sheep.