What are SNPs and how can they affect gene function or phenotype?

• A. SNPs are large inversions.
• B. SNPs always cause disease.
• C. SNPs are only in noncoding regions.
• D. Single-nucleotide polymorphisms can alter amino acid sequences, regulatory motifs, or splicing; they contribute to genetic diversity and disease risk.

Answer: (D)

SNPs are single-nucleotide variations found in DNA across individuals. They can occur in coding regions or in noncoding regions, and their effects depend on where they occur. When a SNP is in a coding sequence, it can change the amino acid encoded (missense), create a premature stop (nonsense), or leave the amino acid unchanged (synonymous), any of which can influence protein function. If a SNP sits in regulatory DNA or affects splice sites, it can alter how much of a gene is made or how the mRNA is processed, changing gene expression levels or producing different mRNA isoforms. Because many SNPs tweak regulation or protein function rather than abolish it entirely, they contribute to genetic diversity and can influence disease risk in various ways. Some SNPs are neutral, but others shift phenotypes by changing protein activity or gene regulation.