13.8: Comparing Copy Number Variations and SNPs
Sequencing of the human genome has opened up several best-kept secrets of the genome. Scientists have identified thousands of genome variations that exist within a population. These variations can be a single nucleotide or a larger chromosomal variation.
Copy number variations or CNVs are the structural variations that cover more than 1kb of DNA sequence. The single nucleotide polymorphism (SNP), on the other hand, is a single nucleotide change or a point mutation that is found in more than 1% of the population. Both CNV and SNPs are immensely valuable in genetic screening studies and kinship analysis.
Forms of CNVs.
There are five forms of CNVs. The first is called a deletion. A loss of a DNA segment can reduce the copy number of a gene or a group of genes. The second is called tandem duplication. Here, a copy of a chromosomal segment is inserted into an adjacent region. The third is called noncontiguous duplication. Here, a chromosomal segment duplicates and inserts into a distant chromosomal region or a different chromosome. The fourth form is called Multiallelic CNV. A segment of DNA duplicates several times and results in the formation of multiple alleles of a gene. The fifth form is called complex rearrangement. Here a segment of DNA duplicates and inverts before being inserted back into the same or different chromosome.
Single Nucleotide Polymorphism
Single Nucleotide Polymorphism or SNP is another type of genomic variation involving alterations in a single nucleotide base. Scientists have identified thousands of SNPs throughout the human genome, and they are routinely used as genetic markers for inherited diseases and forensic analysis.
Based on their application, SNPs are divided into four types. Identity-testing SNPs are used to differentiate people and eliminate people from familial connections. Lineage informative SNPs are tightly linked SNPs that help identify missing individuals in a familial analysis. Ancestry informative SNPs help establish a person’s ancestry and connect it with their phenotypic characteristics. Phenotype informative SNPs establish the probability of inheriting a particular phenotype, such as skin color, eye color, etc.