Genotyping is a scientific process used to identify specific differences in an individual’s genetic makeup by examining an organism’s DNA sequence and comparing it to another individual’s sequence or a reference. This method is fundamental for understanding how genetic variations contribute to unique traits and characteristics.
The Genetic Blueprint
DNA carries genetic instructions, and within it are genes, segments that provide instructions for building and maintaining an organism. While much of our DNA is similar across individuals, subtle differences exist, known as genetic variations. These variations can take several forms, with single nucleotide polymorphisms (SNPs) being the most common. A SNP occurs when a single DNA building block (A, T, C, or G) is changed at a specific genome position. Other variations include insertions, where extra DNA segments are added, or deletions, where segments are missing.
Steps in the Genotyping Process
The genotyping process begins with obtaining a biological sample from an individual. Common sources include blood, saliva, or cheek swabs, which are often collected non-invasively.
Once collected, DNA extraction isolates the DNA from other cellular components in the sample. This process purifies the DNA, making it accessible for subsequent analysis. The quality and quantity of the extracted DNA are important for successful genotyping.
Following extraction, specific DNA regions of interest are amplified, meaning many copies are made. This amplification is performed using Polymerase Chain Reaction (PCR). PCR creates millions of copies of a targeted DNA segment, ensuring there is enough material for accurate detection of genetic variations. The amplified DNA is then ready for analysis to pinpoint specific variations.
Key Genotyping Technologies
Several technologies are employed to identify genetic variations. PCR-based assays utilize the amplification process to detect specific variations. In these assays, specially designed DNA primers bind to the variant of interest, allowing for its selective amplification and identification. This method is used for detecting known SNPs or small insertions and deletions.
DNA microarrays, also known as SNP arrays, provide a high-throughput platform for detecting thousands to millions of SNPs simultaneously. These arrays consist of a solid surface with microscopic spots, each containing a unique DNA probe. When a sample’s DNA is applied, it binds to complementary probes on the array. The intensity of the binding signal then indicates the presence of specific variations.
Next-Generation Sequencing (NGS) offers a comprehensive approach by reading the exact DNA code. While whole-genome sequencing reads an entire genome, NGS for genotyping typically focuses on targeted regions or a subset of the genome. This technology generates millions of short DNA reads. These reads are then aligned to a reference genome to identify variations, including SNPs and insertions/deletions.
Understanding Genotyping Results
Genotyping results provide specific information about an individual’s genetic makeup at targeted locations. They reveal the presence or absence of particular genetic variations, such as SNPs, in the analyzed DNA regions. For each genotyped site, the result typically indicates which version, or allele, of the variation an individual possesses. This information highlights the genetic differences between individuals. These findings can indicate a genetic predisposition or a specific inherited trait, providing insights into an individual’s unique biological characteristics.