chapter  15
12 Pages


WithUlrika Liljedahl and Ann-Christine Syva¨nen

The DNA sequences of different individuals are identical to 99.9% (1,2). The remaining variable 0.1% consists mainly of single-nucleotide polymorphisms (SNPs), which explain a large fraction of the inter-individual differences in phenotype between populations and individuals. Depending on the location of an SNP, the phenotypic consequences of it may differ. The SNPs within the protein coding regions of a gene may alter an amino acid and thus change the structure and function of the protein. A nucleotide change can also result in a synonymous change that has no effect on the amino acid in the protein. The SNPs in regulatory, non-coding regions of a gene may affect the binding of transcription factors and thereby the expression level of genes (3). The majority of the SNPs are located in the non-coding parts of the genome, where they have no currently known functional effect.