DNA Basics: Demystifying the Jargon

Whether you’re just stepping into the world of DNA testing or you’ve been here a while, there are probably a few key words or phrases that befuddle and bemuse you. From chromosomes to single nucleotide polymorphisms, sometimes the jargon can feel a little overwhelming!

This week we’re exploring the key terms and phrases you might have seen as you navigate your DNA journey, aiming to help you cut through the fog to understand even more about your results, your matches, and your body.

DNA

Let's begin at the beginning. DNA stands for deoxyribonucleic acid. It’s a molecule twisted into the famous double-helix shape and it contains the genetic instructions for all known living things. Your DNA is unique to you but we do share a lot of it in common with other people, animals, and even bananas!

Chromosome

When a cell in your body divides, the long strands of DNA are at risk of getting tangled up with one another. To avoid this, they coil themselves up into tight packages called chromosomes. Humans have 23 pairs of chromosomes, with the final pair typically denoting sex. You have probably seen this written as XX (female) and XY (male).

Gene

Genes are functional parts of DNA that carry specific instructions for your body. Each one can influence your traits, such as your eye colour, your height, or creating collagen in your skin.

Allele

Each one of your genes can come in a number of varieties, and each variation at a specific point in your DNA is called an allele. In some cases there’s a simple choice of one or the other - pea plants have one allele for purple and one allele for white in their flowers - but a lot of the time it’s far more complex.

Nucleotide

Nucleotides are often called the building blocks of DNA, and are made of 3 parts: a sugar, a phosphate, and a nitrogenous base. Nucleotides snap together - a little like lego bricks with different shapes and colours - in specific sequences that encode genetic information. The order of each nucleotide is crucial, because it determines the instructions for the building and functioning of living organisms.

Nitrogenous Bases

The building blocks that make up DNA, there are only 4 nitrogenous bases that are repeated over and over again to make your genome: Adenine (A), thymine (T), cytosine (C), and guanine (G). The bases pair up in specific combinations - A with T and C with G.

Single Nucleotide Polymorphism (SNP)

Each nucleotide occurs at a specific point on a person’s genome, so can be compared between individuals. A single nucleotide polymorphism is a variation that occurs on a single nucleotide at a specific position in the genome. They serve as common genetic markers for studying traits and diseases across populations.

Genome

The genome is the entire set of an organism’s genetic material. This includes genes, regulatory sequences, and non-coding DNA regions. It’s like a complete instruction manual for building and operating a living thing. The human genome was mapped in its entirety for the first time in 2003, after a 13 year project.

Genetic Variation

Genetic variation refers to the differences between individuals within a population - like finches on an island having differently shaped beaks to suit different ecological niches. This variation is the driving force behind evolution, as variations that are beneficial allow an individual to survive and pass down their traits to the next generation.

Genotyping

Genotyping involves analysing specific genes or DNA sequences to determine variations they have inherited from their parents. These variations can be involved in determining things like your eye colour, your risk of developing certain diseases, or - if you test with Living DNA - your ancestry and wellbeing traits.

SNP-Chip

A ‘chip’ (or array) scans hundreds of thousands of positions throughout your genome. These positions, known as Single Nucleotide Polymorphisms (SNPs), are highly variable across populations and individuals, and allow us to explore with high resolution your unique genetic profile.

Genotype and Phenotype

Genotype refers to the genetic makeup of an organism, while phenotype refers to characteristics that come from interaction between the genotype and the environment.

Mitochondrial (mtDNA)

mtDNA is a unique genome that’s found in the mitochondria of your cells, which is inherited exclusively from the maternal lineage. It’s invaluable for tracing maternal ancestry and understanding human evolutionary history.

Mitochondria

Every teenager in a biology class will be able to tell you that “the mitochondria is the powerhouse of the cell,” but what does this really mean? In order to perform their functions, your cells need energy, which is produced by mitochondria. They convert nutrients from food into a form of energy called adenosine triphosphate (ATP). Some cells work harder than others - such as those in your muscles or liver - and they contain more mitochondria than others to generate the energy they need.

Y-DNA

Y-DNA is inherited paternally. It is found only on the Y chromosome, and so is only found in genetically male individuals. Your haplogroup can be used to trace your paternal lineage and is used in studying population genetics.

Haplogroups

Haplogroups are genetic population groups that share a common ancestor, identified by specific DNA markers. These markers can be inherited through maternal (mitochondrial) or paternal (Y-DNA) lineages, and provide insights into deep ancestral origins and migration patterns. By studying haplogroups, researchers can trace human evolutionary history, map population movements, and uncover connections between both individuals and populations across geographical and historical contexts.

Autosomal

Your autosome is all of the chromosomes not involved in determining an individual’s sex. This varies between different animals, but in humans it’s the first 22 pairs of chromosomes. Autosomal DNA testing analyses genetic information from those chromosomes to provide insights into ancestry, health, and in some cases health conditions that are not related to genetic sex. This type of testing is particularly useful for tracing both maternal and paternal lineages and understanding inherited traits across all ancestors, regardless of their sex.

Recombination

Recombination mixes up genes from two parents into a new individual. It’s like swapping pieces between matching puzzles to create new combinations. This swapping process adds variety to offspring, as each one will receive a unique combination of their parents’ DNA. It helps species to adapt and evolve over time by introducing new traits and abilities.

Centimorgan

Centimorgans are usually used in family matching to determine how closely or distantly related two people are. Essentially, the more centimorgans you have in common with someone, the more closely you are related. We use ranges to estimate relationships because, due to the random nature of inheritance (see Recombination and Genetic Drift), the exact amount of DNA inherited from a specific ancestor varies between individuals.

Genetic Drift

This term describes the process by which certain traits are lost or become common within populations over just a handful of generations. Imagine you had a bowl of marbles, 50 blue and 50 red. This represents a single individual in a population. If you select a random 50 marbles from your 100 you might expect to pick out an equal number of red and blue, but what’s more likely to happen is that you end up with more of one than the other. You may even select only one or two red with the rest being blue. In the following generation, it will be much harder to select a red marble, with the chances being quite high that you pick only blue marbles.

This can also explain why all traces of a specific ancestor can be lost within just a small handful of generations. You may be expecting to see 25% of your ancestry from your Scottish grandmother but only actually get 5%, for example.

Along all of your autosomal DNA you have two copies of each gene - one from each parent. Ideally, these will be different versions of the same gene (see heterozygous), but they can be the same. In some cases, having the same version of a gene from each parent can cause illnesses. For example, if both parents carry one allele for cystic fibrosis, there is a 1 in 4 chance that their child will inherit that allele from both parents and therefore be born with cystic fibrosis.

There are higher rates of homozygosity in endogamous populations, where the chances that a couple will have genes in common is higher than average.

Heterozygous

The opposite of homozygosity, heterozygosity means inheriting different copies of the same gene from each parent.

If both parents carry one allele for cystic fibrosis, there is a one in 4 chance their child will inherit no cystic fibrosis alleles, and a 1 in 2 chance they will inherit the allele from one of their parents but not the other. Neither of these outcomes will mean that the child is born with cystic fibrosis.

If only one parent carries the allele for cystic fibrosis, there is no chance of their offspring being born with the illness.

Centromere

The constricted part at the centre of a chromosome, where the points of the X shape meet. It plays an important part in helping DNA divide and split during both meiosis and mitosis (cell division).

Telomere

At the end of each chromosome there is a series of repetitive DNA sequences that let DNA repair sequences know where the end is, and preventing them from mistaking the end points for breaks. Every time a cell divides, the telomeres get shorter. This means that those in the cells of a newborn are much longer than those of a teenager, and a teenager’s are much longer than those of someone in their 70s or 80s. It is thought that they play an important part in the ageing process.

Junk DNA

Some DNA along your genome has no biological function. This is known as ‘junk DNA’. It’s mostly comprised of pseudogenes (segments of DNA that look like genes but cannot code for protein), and fragments of transpons (DNA sequences that can change their position in the genome and affect mutations), and viruses.

Endogamous

Endogamy describes the practice of marrying within your own group. This can happen based on religion, social status, or heritage. The practice can help to keep cultural traditions and values alive within a community - such as speaking a local dialect - but too much endogamy over the generations can limit genetic diversity and lead to an increased risk of inherited genetic disorders. The royal families of Europe suffered from the effects of extreme endogamy in centuries past, leading to the famous Habsburg Jaw among other more debilitating conditions.

We’d love to hear from you about more terms and phrases that you’re having trouble understanding, so we can expand this article in the future. If there’s anything you’d like to know, please get in touch with help@livingdna.com, and mention this blog in your message.