Comparative study of single nucleotide polymorphisms (SNPs) of a candidate growth gene (IGF-I) in Oreochromis niloticus and Sarotherodon melanotheron

In teleost fishes, the regulation of growth performance by the GH and IGF system also seems to be highly conserved. Adult Oreochromis niloticus (Nile tilapia) could reach up to 60 cm maximum length while Sarotherodon melanotheron (black chin Tilapia) has a maximum length of 28 cm. This study describes the analysis of Single Nucleotide Polymorphism in isolated, amplified, and sequenced DNA from two common Tilapia species (O. niloticus and S. melanotheron) with the aim of identifying genetic variation and single nucleotide polymorphisms (SNPs) in one of the main genes, Insulin like growth Factor-1 (IGF-I), related to growth in the Tilapia species. The extracted DNA from the clipped caudal fins of the Tilapia species samples using Sambrook and Russell’s modified chlolorophenol/isoamyl alcohol DNA extraction method were further amplified in a thermal cycler with designed IGF-I forward and reverse primers of 447 bp which were subsequently sequenced with an automated analyzer. The PCR product was separated on 1.5% ethidium stained agarose gel electrophoresis and the bands revealed on the gel were all of the same length (447 bp). The Sequence alignment revealed a total of five single nucleotide polymorphisms which were detected in the forward reaction at the positions 181, 199, 328, 362 and 369 of the sequences and in the reverse reaction at positions 18, 20, 54, 183 and 201. A total of 138 amino acid sequence was translated from the DNA sequence with variations sequence at positions 1, 3, 4, 61, 67, 121 and 123. These results showed variations among these two fish species which could explain differential growth performance between them.   Key words: Single nucleotide polymorphism (SNP), Oreochromis niloticus (ON), Sarotherodon melanotheron (SM), Tilapia and insulin-like growth factor (IGF).