Complementary single-nucleotide polymorphisms (SNPs) may not be distributed equally between two DNA strands if the strands are functionally distinct, such as in transcribed genes. In introns, an excess of A<-->G over the complementary C<-->T substitutions had previously been found and attributed to transcription-coupled repair (TCR), demonstrating the valuable functional clues that can be obtained by studying such asymmetry. Here we studied asymmetry of human synonymous SNPs (sSNPs) in the fourfold degenerate (FFD) sites as compared to intronic SNPs (iSNPs).
Qu, H. Q., Lawrence, S. G., Guo, F., Majewski, J., & Polychronakos, C. (2006). Strand bias in complementary single-nucleotide polymorphisms of transcribed human sequences: Evidence for functional effects of synonymous polymorphisms. BMC Genomics, 7. https://doi.org/10.1186/1471-2164-7-213