Unlocking the Language of Genetics: Key Terms & Definitions
Navigating the World of Genetics: Key Terms to Understand
Before diving into genetics, it’s helpful to understand some foundational terms. Let's go through a few key concepts in genetics, including DNA, alleles, genotypes, and more.
What is DNA?
DNA (Deoxyribonucleic Acid) is the molecule that contains the instructions needed for an organism to grow, develop, and function. It looks like a twisted ladder, a structure called a double helix, with a "backbone" made of sugar and phosphate, and "steps" consisting of nitrogenous base pairs.
There are four bases in DNA:
- Guanine (G)
- Cytosine (C)
- Adenine (A)
- Thymine (T)
These bases pair up in a specific way: G pairs with C, and A pairs with T. Together, these base pairs make up the code that defines every living thing on Earth.
What is a Genome?
The genome is the complete set of DNA found in an organism. It contains all the genes and non-coding regions, representing the entire "instruction manual" that makes you who you are. Humans have about 20,000-25,000 genes spread across their DNA, which provide the blueprint for proteins and many bodily functions.
However, genes are only part of the story. The genome also contains millions of genetic variants—approximately 4 to 5 million in each person. These variants, which include single nucleotide polymorphisms (SNPs), insertions, deletions, and larger structural variations, are differences in the DNA sequence that make each person unique. It's important to note that genes and genetic variants are different: genes are specific sequences that code for proteins, while genetic variants are changes or differences in the DNA sequence that can affect how those genes function or are expressed.
What is an Allele?
An allele is a variant form of a gene. For each gene, you inherit one allele from your mother and one from your father. Different alleles can lead to different traits.
For example, consider a gene associated with the regulation of serotonin, a neurotransmitter linked to mood and anxiety. This gene may have two common alleles:
- A (which may lead to increased serotonin levels)
- G (which may lead to decreased serotonin levels)
Depending on which alleles an individual inherits, they may be more or less predisposed to symptoms of anxiety.
What is a Genotype?
A genotype is the specific combination of alleles you have for a particular gene. It’s like a blueprint that influences your traits. In the case of the serotonin gene, an individual can have the following genotypes:
- AA (homozygous for the A allele) – They may have higher serotonin levels, potentially leading to lower anxiety.
- AG (heterozygous) – They may have a moderate level of serotonin, resulting in an intermediate risk for anxiety.
- GG (homozygous for the G allele) – They may have lower serotonin levels, which could increase their susceptibility to anxiety disorders.
In this example, the genotype (AA, AG, or GG) directly influences an individual’s predisposition to anxiety.
Homozygous and Heterozygous
Homozygous and heterozygous refer to the genetic makeup of an individual regarding a specific gene.
- Homozygous means that an individual has two identical alleles for a particular gene. For example, if both alleles are the same (AA or gg), the individual is homozygous for that gene.
- Heterozygous means that an individual has two different alleles for a particular gene. For example, if one allele is A and the other is G (AG), the individual is heterozygous for that gene.
These genetic combinations can affect how traits are expressed, influencing an individual’s characteristics or susceptibility to certain conditions.
What is Gene Expression?
Gene expression is the process by which the information in a gene is used to create proteins or other products that contribute to a cell's function. Not all genes are "turned on" all the time—some are expressed only under certain conditions or in specific types of cells.
What is Genetic Imputation?
Genetic imputation is a statistical technique used to predict the genetic variations that are not directly tested. When you get your DNA analyzed, there are often gaps in the data due to limitations in the testing process. Imputation helps fill in these gaps by using reference populations, increasing the usefulness of your genetic information.
What is a Polygenic Risk Score?
A polygenic risk score (PRS) estimates your likelihood of developing a certain trait or disease by combining the effects of many genetic variants. Unlike single-gene conditions, which are controlled by one gene, many common traits—like height or risk for heart disease—are influenced by multiple genes. PRS helps assess these complex risks.
What is a SNP (rsID)?
A single nucleotide polymorphism (SNP) is a variation at a single position in DNA. SNPs are the most common type of genetic variation among people. Each SNP represents a difference in a single DNA building block, called a nucleotide.
An rsID is a unique identifier given to an SNP. It helps researchers and genetic testing companies reference specific SNPs. For example, rs4988235 is an SNP associated with lactose intolerance. Knowing your SNPs can provide insights into traits and health risks.
By understanding these terms—DNA, alleles, genotypes, gene expression, genetic imputation, polygenic risk score, and SNPs—you’re better equipped to explore the complexities of genetics. This foundational knowledge helps unlock insights into how genes shape our traits, health, and individuality.
If you have questions about your results, feel free to reach out to DecodyGPT, our built-in AI health coach, for personalized guidance. Alternatively, you can speak directly with your healthcare practitioner or consider purchasing consultations with a SelfDecode practitioner for more in-depth support.