Single Nucleotide Polymorphisms and Haplotype Analyses in Tilapia Fish Inferred from mtDNA D-loop and Cyt-b Regions
E. V. Ikpeme
Animal Genetics and Genomics Unit, Department of Genetics and Biotechnology, University of Calabar, PMB 1115, Calabar, Nigeria.
O. U. Udensi
Plant Resource Management and Genomics Unit, Department of Genetics and Biotechnology, University of Calabar, PMB 1115, Calabar, Nigeria.
E. E. Ekerette *
Animal Genetics and Genomics Unit, Department of Genetics and Biotechnology, University of Calabar, PMB 1115, Calabar, Nigeria.
M. O. Ozoje
Animal Genetics and Genomics Unit, Department of Genetics and Biotechnology, University of Calabar, PMB 1115, Calabar, Nigeria and Department of Animal Breeding and Genetics, Federal University of Agriculture, PMB 2240, Abeokuta, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
Objective: This research was aimed at analysing single nucleotide polymorphisms and haplotypes on D-loop and Cyt-b regions of the mitochondrial DNA of tilapia fish.
Methods: Fifteen and thirteen tilapia fish were obtained from two populations, south-south (Domita farm) and south-west (Odeda farm). DNA extraction from fish tissue was done using Quick-gDNATM mini Prep kit after which PCR amplification was carried out. Sequencing of the two mtDNA regions were done using forward primer 5’- GGATTYTAACCCYTRCCCC- 3’ and reverse 3’-AGTAAGTCAGGACCAAGCC-5’ for D-loop and 5’-GGATTTTAACCCTTACCCC-3’ and 3’-AGTAAAGTCAGGACCAAGCC-5’ for Cyt-b region. Statistical analyses were carried out on the aligned sequenced data using MEGA version 6.06, Dnasp 5.1, Codon code aligner 6.06 as well as NETWORK 4.6.1.1.
Results: mtDNA polymorphism was highest in the D-loop of South-South (SS) population with 176 polymorphic sites, while South-West (SW) population had 162 polymorphic sites translating to 176, 162 and 144 SNPs with higher non-synonymous substitutions than synonymous substitutions. Haplotype diversities (Hd) were 1.00 ± 0.024 and 1.00 ± 0.030 while nucleotide diversities were 0.168 ± 0.086 and 0.161 ± 0.084 for D-loop of SS and SW populations, respectively. For Cyt b region, haplotype and nucleotide diversities were 0.91 ± 0.003 and 0.051 ± 0.016. Positive selection was more on mtDNA D-loop of tilapia sampled from SS than those from the SW as well as Cyt-b region of tilapia fish from SS. 28 haplotypes were identified among the tilapia from SS and SW with no shared haplotypes while 9 haplotypes were identified from the Cyt-b region with haplotypes 4, 5, 6 and 7 shared between species. Median-joining network analysis revealed population-based clustering pattern. The demographic expansion was not significant using Tajima's D and Fu's F statistics.
Conclusion: Higher SNPs were revealed in mtDNA D-loop when compared with mtDNA Cyt-b region of tilapia fish.
Keywords: SNPs, haplotype, mtDNA D-loop and Cyt-b, tilapia fish, variation