SNPidentifier

SNPidentifier predicts single nucleotide polymorphisms (SNPs) within expressed sequence tag (EST) clusters to identify polymorphic sites for quantitative trait loci mapping, association studies, and marker-assisted selection, including applications in Litopenaeus vannamei (Pacific white shrimp).

Key Features:

• Compatibility with CAP3 clusters: Processes EST clusters generated by the CAP3 program and identifies potential SNPs without requiring chromatogram sequence quality information.
• Quality control: Applies a poor-quality nucleotide (N) frequency threshold of <0.1 and trims the first 10 bases from each sequence.
• Conservative SNP prediction criteria: Calls SNPs only if the minor allele frequency >0.1, the minor nucleotide is observed at least four times, and the 15 bases flanking each candidate SNP exactly match the consensus sequence.
• Tandem repeat handling and dataset processing: Sequences are manually screened and masked for tandem repeats prior to CAP3 clustering, exemplified by analysis of 25,937 ESTs producing 3,532 contigs.
• Prediction output and validation statistics: In the L. vannamei study, the tool predicted 504 SNPs from 141 contigs and validation by sequencing 18 individuals from three lines confirmed 44% (17 out of 39) of tested SNPs.

Scientific Applications:

• Quantitative trait loci (QTL) mapping: Identification of SNPs in EST clusters to support QTL mapping in species lacking full genomic sequences.
• Association studies: Discovery of polymorphic sites for genotype–phenotype association analyses.
• Marker-assisted selection: Generation of SNP markers to inform marker-assisted selection in breeding programs, including aquaculture species such as L. vannamei.
• Genetic studies in non-model species: Enables SNP discovery from EST data where whole-genome sequences are unavailable.

Methodology:

Sequences are manually screened and masked for tandem repeats, clustered with CAP3, processed without chromatogram quality input, trimmed by 10 bases, filtered for N frequency <0.1, and candidate SNPs are called using criteria of minor allele frequency >0.1, ≥4 observations of the minor nucleotide, and exact 15-base flanking matches to the consensus.