Our genetic makeup, deoxyribonucleic acid (DNA), contains instructions that guide the development and function of every living organism. Differences in the DNA sequence, known as DNA variants, are a fundamental aspect of human genetic diversity. Understanding DNA variants helps explain why individuals differ in traits and how certain health conditions may arise.
Understanding DNA Variants
A DNA variant represents a change in the specific sequence of nucleotides, which are the building blocks or “letters” of the genetic code. Imagine DNA as a long instruction manual; a variant is simply a typo or a reordering of a few letters within that manual. These changes can range from a single nucleotide alteration, known as a single nucleotide polymorphism (SNP), to larger changes involving the insertion or deletion of multiple nucleotides.
Variations can also involve larger structural changes, such as copy number variations (CNVs), where entire sections of DNA are duplicated or deleted. Some variants are common within a population, while others are quite rare. These variations can occur in both the protein-coding regions of genes and the non-coding regions that regulate gene activity.
How DNA Variants Arise
DNA variants arise through several biological mechanisms. One common source is random mutations, which are errors that occur spontaneously during DNA replication. Despite repair systems within cells, occasional mistakes in copying the genetic code can become permanent changes in the DNA sequence.
Environmental factors can also induce DNA variants. Exposure to mutagens, such as certain chemicals or ultraviolet (UV) radiation from the sun, can damage DNA and lead to alterations in its sequence. If these damages are not repaired by the cell’s internal mechanisms, they can result in new variants.
Many DNA variants are inherited, meaning they are passed down from parents to their offspring. These hereditary variants are present in the parent’s egg or sperm cells and are then incorporated into the child’s cells. Additionally, some variants are considered “de novo,” meaning they appear for the first time in a child and are not found in either parent’s DNA. These de novo variants can occur in a parent’s germ cells or in the fertilized egg.
Impact of DNA Variants
The effects of DNA variants on an individual can range from having no observable impact to influencing health and traits. Many variants are considered neutral, meaning they do not alter the function of a gene or the protein it produces. For instance, some variants in DNA sequences do not change the amino acid sequence of a protein, making them “silent” changes.
Some DNA variants can be beneficial, offering an advantage to an individual. For example, certain variants might provide resistance to specific diseases, helping an individual survive in particular environments. These advantageous variants can become more common in a population over generations through natural selection.
Conversely, some variants can be harmful, contributing to disease susceptibility or directly causing genetic disorders. When a variant changes a gene’s instructions, it can lead to a protein malfunctioning or not being produced at all. This disruption can impact normal development or result in a health condition, such as cystic fibrosis, which is caused by a deletion in the CFTR gene. The impact of a variant often depends on its specific location within the genome, the particular gene it affects, and how it interacts with other genes and environmental factors.
Identifying DNA Variants
Scientists and clinicians employ several techniques to identify DNA variants. Genetic testing involves analyzing an individual’s genetic material. These tests can involve examining chromosomes, DNA, or RNA to detect genetic changes.
Genomic sequencing involves “reading” the entire DNA sequence of an individual to pinpoint differences from a reference genome. Next-generation sequencing (NGS) allows for the simultaneous analysis of millions of DNA sequences, making it effective for detecting various types of variants, including SNPs and insertions/deletions. Another technique, microarrays, can be used to detect larger changes like copy number variations across many genes or regions simultaneously.