Exon 2 polymorphism of the ß-lactoglobulin gene by restriction enzyme in three Iraqi sheep breeds

Beta-lactoglobulin (BLG) is an essential protein in whey. This experiment aimed to study the genetic variation in exon 2 of the beta-lactoglobulin gene in three local Iraqi sheep breeds (30 Al-Hamdani, 30 Al-Karadi, and 30 Al-Awassi). 5 ml of blood were collected from animals of each breed. Results of the migration of DNA fragments digested with the restriction enzyme (RsaI) revealed three genotypes: aa, Aa, and AA. It was found that the distribution ratios of the genetic structures of the three breeds, Al-Hamdani (0.47, 0.4, 0.13), Al-Karadi (0.47, 0.34, 0.10) and Al-Awassi (0.40, 0.50, 0.10), and the distribution ratios of the alleles (A) and (a) were for Al-Hamdani (0.67, 0.33) Al-Karadi (0.68, 0.32) and Al-Awassi (0.65, 0.35), the Chi-square values ​​were significantly different for the three breeds. The electrophoresis data were analysed to calculate the observed and expected homozygous and heterozygous allele numbers, the influential allele numbers, and Shannon's index (I) for each sheep breed. The values ​​of the observed and expected heterozygote alleles for the Al-Hamdani breed were (0.4000, 0.4250), Al-Karadi (0.4333, 0.4401) and Al-Awassi (0.5000, 0.4627). The number of influential alleles was for the Al-Hamdani breed (1.800), Al-Karadi (1.736, and Al-Awassi 1.8439. Shannon's index values showed a decrease in the three breeds: Al-Hamdani (0.6365), Al-Karadi (0.6243), and Al-Awassi (0.6474), with Al-Awassi having the highest estimate among the three breeds. The genetic affinity tree diagram shows greater genetic affinity between the Al-Hamdani and Al-Karadi breeds than between the Al-Awassi breed. The results show a higher prevalence of dominant and heterozygote genotypes, a higher proportion of the (A) allele over the (a) allele, higher observed heterozygote allele values for the Al-Hamdani and Al-Karadi breeds, and higher expected heterozygote allele values for the Al-Awassi breed.