9 Sep, 2019

Genetics terms you need to know

If you’ve got an interest in genetics or you’re planning on doing a DNA test, here’s some of the most important terms you’ll need to know.

In preparation for our kit launch, we thought it would be helpful to provide more information about genetics so you can choose the kit that works best for you. This blog post is full of terms and definitions to help you understand the process of DNA testing a little bit better and hopefully give you some more knowledge about genetics in general.

DNA

This is probably the most important one. DNA, which stands for Deoxyribonucleic acid, is a molecule that contains information which codes for the building and maintenance of an organism. Almost every cell in your body contains the same DNA and this information is located in the cell’s nucleus and mitochondria.

DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. There are four different nitrogen bases: Adenine (A), Thymine (T), Guanine (G) and Cytosine (C) and the order of these bases determines the instructions for DNA. Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people!

Base pair

DNA bases pair up with each other (A with T and C with G) to form units called base pairs. As described in the DNA section, these bases are also attached to a phosphate molecule and a sugar molecule which together makes a ‘nucleotide’ molecule. These nucleotides are arranged in a long stand which then joins at the bases to another strand, forming a spiral shape called a ‘double helix’.

Genotyping

The word “genotype" refers to all the genes that make up an organism or, in other words, an organism’s genetic makeup. However, it can also be used to refer to all the alleles that are carried by an organism; alleles are variations of the same gene (for more info see the definition for ‘allele’). Genotyping is the process of finding differences in the genotype of an individual by examining their DNA sequence using biological assays and comparing it to a different sequence or set of sequences.

Sequencing

DNA or genetic sequencing is the process that’s used to determine the sequence of base pairs in an individual's DNA. There are several methods and technologies that are used to sequence DNA and determine the order of the four bases in someone's DNA. You can find out more about the different types of sequencing here.

SNP

SNP or ‘snip’ stands for single-nucleotide polymorphism- which sounds more complicated than it is! A SNP is just the variation in bases, Adenine (A), Thymine (T), Cytosine (C), and Guanine (G), between members of a species or paired chromosomes in an individual

We use SNPs to help you learn more about your health in our personalised reports, where you can find out which SNPs you have in certain locations and what they mean.

Chromosome

Chromosomes are structures made up of DNA which have been tightly coiled many times around proteins called histones. Chromosomes are found in the nucleus of every cell; human cells contain 46 chromosomes, made up of 23 pairs. One half of each pair is inherited from the mother and one from the father.

Gene

By definition a gene is ‘the basic physical and functional unit of heredity’. Genes are made up of DNA and can act as instructions to make proteins. Not all genes code for proteins, however. Genes in humans can vary in size massively, from just a few hundred DNA bases to more than 2 million bases. It’s also been estimated by The Human Genome Project that humans have between 20,000 and 25,000 genes altogether.

Allele

An allele is a variation of a gene. Humans inherit two alleles for every gene, one from their mother and one from their father; because humans have two alleles at each gene locus, they’re called ‘diploid organisms’. Each pair of alleles also represents the genotype of a specific gene - something you can find out more about in our personalised reports.

Some alleles are dominant or recessive. When an organism is heterozygous at a specific locus and carries one dominant and one recessive allele, the organism will express the dominant phenotype.

Imputation

Many types of DNA kit use genotyping arrays rather than whole genome sequencing. This process only tests a small number of sites - on average about a few letters in every thousand - and they miss out a lot of information because they only focus on the areas where humans tend to be different from one another.

A statistical technique called imputation can be used to ‘fill in the blanks’ for the letters in between. Imputation provides a ‘free upgrade’ to genotyping data, but it is far from perfect. Imputation is unreliable for rare genetic variants, so it will not transform a genotyping test into a whole genome sequence, but it is still a valuable tool.

To find out more about imputation, read our blog post.

Now you're all set

Hopefully, these definitions will give you a little bit of a further insight into genetics; whether your a student, a customer or just curious - it’s great to learn and discover every day. But if you're still hungry for more, check out the rest of our blog posts or follow us on social media to be the first to hear about our podcasts, blog posts and updates.

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