Single Nucleotide Polymorphisms (SNPs), pronounced 'snips', are the most abundant type of genetic variation in humans, occurring approximately every 1,000 base pairs. They represent a substitution of a single nucleotide (A, T, C, or G) at a specific position in the genome. While many SNPs have no observable effect on health or development, others can influence an individual's susceptibility to diseases or their response to drugs. Their high frequency and stable inheritance make them invaluable for genetic association studies and population genetics.

Insertions and Deletions, collectively known as Indels, are another significant class of genetic variants. An insertion involves the addition of one or more nucleotides into the DNA sequence, while a deletion involves the removal of one or more nucleotides. The impact of indels depends on their size and location. Small indels, especially those within coding regions, can cause frameshift mutations, altering the entire downstream amino acid sequence of a protein, often leading to a non-functional protein. Larger indels can affect gene regulation or even lead to the loss or duplication of entire genes.

Copy Number Variations (CNVs) are structural variations that encompass the deletion or duplication of larger DNA segments, typically ranging from 1 kilobase (kb) to several megabases (Mb). Unlike SNPs and small indels, CNVs affect a larger portion of the genome. Duplications can lead to an increased dosage of genes within the affected region, potentially altering cellular function. Conversely, deletions can result in the loss of genes or regulatory elements. CNVs are implicated in a wide range of genetic disorders, including developmental disabilities, cancer, and autoimmune diseases.

Structural Variants (SVs) represent a broad category of genomic alterations that involve larger segments of DNA, often affecting chromosome structure. This category includes inversions (where a segment of DNA is flipped), translocations (where a segment of DNA moves from one chromosome to another), and large insertions or deletions. SVs can disrupt gene function, alter gene dosage, create novel fusion genes, or lead to chromosomal instability. Their detection often requires specialized sequencing technologies and analytical approaches due to their size and complexity.