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Genomics 101: What is a genetic change?

By Florence Cornish on

In this series, ‘Genomics 101’, we go back to basics and explore some of the most important topics in genomics. In this blog, we explain the term ‘genetic change’, what can cause them, and how they may affect our health.

First things first, what do we mean by genetic change?

A genetic change, also known as a genetic variant, is when a change has occurred in the sequence of someone’s DNA.

DNA is a molecule found in all living things. It carries the genetic information that we need to survive, function and grow, like an instruction manual.

When there are glitches in this instruction manual, or ‘genetic changes’, this can impact our health and development.

How does this happen?

DNA sequences are made up of 4 different ‘bases’, which we represent using the letters A, T, C and G.

The cells in our body can read this sequence, almost like reading a book, and produce the different proteins we need to survive.

Sometimes, the order of letters in the sequence gets muddled. Letters can be replaced, removed, or extra ones can be added.

This can lead to changes in the proteins that are produced.

To learn more about changes in our DNA, check out the Unique guide on interpreting genetic test results.

Can we inherit genetic changes?

Yes, we can inherit genetic changes from either or both of our parents.

This occurs when a parent carries a genetic change that ends up in their sperm or egg cells. When the sperm and egg join at conception, the genetic change than gets passed down to their child.

We call these types of changes ‘germline mutations’, and they will be present in almost every cell of the child’s body throughout their life.

Are all genetic changes inherited?

Good question! The answer is no, not all genetic changes are inherited.

Any changes that are present in a person but not present in either parent are known as ‘de novo’ changes.

These can arise during early development before someone is born, but they can also happen later in life.

If they occur very early, for example as an embryo, de novo changes can affect almost every cell in the body, including egg or sperm cells.

This means that people with de novo changes acquired very early in development can pass these changes on to their children in the future.

What about genetic changes that occur later in life?

De novo changes that occur later in life are called ‘somatic changes’.

These cannot be passed down from parent to child because they do not affect the egg or sperm cells.

So, what causes genetic changes to happen?

Most genetic changes occur during cell replication. This is when cells in the body replicate and divide and, allowing for us to grow and develop, and for our tissues to regenerate.

During cell replication, the cell must make a copy it of its DNA. Sometimes, this new copy doesn’t quite match the original, and may have extra bases, missing bases, or other changes in the sequence.

Our cells have mechanisms to repair these, however, they aren’t always perfect and not all changes are corrected. When cells with these genetic glitches go on to replicate, the change becomes present in more and more cells in the body.

Can external factors cause genetic changes?

Yes, some external factors can damage DNA, causing a genetic change.

These factors are known as ‘mutagens’, and examples include dangerous chemicals or radiation.

All genetic changes caused by external factors are somatic, and so cannot be passed down to children, unless they are caused by very high exposure.

So, how do genetic changes cause rare conditions?

As we mentioned earlier, genetic changes can affect the proteins that our body produces.

If a genetic change causes a protein to be faulty or non-functioning, this can cause problems for our health.

Genetic changes can also affect the amount of protein produced, or lead to production at the wrong time in the wrong cells. All of this can also have implications for our bodies.

Can you give an example?

Sure! An example of a rare condition caused by an inherited genetic change is cystic fibrosis.

People with cystic fibrosis have thick, sticky mucus which builds up in their body, often clogging their airways and causing damage to their organs.

The condition is caused by changes in a gene called CFTR, which provides instructions for a protein that helps to keep our mucus thin and free flowing.

When this protein doesn’t function as expected, mucus becomes thicker and much more viscous, in turn causing the symptoms of cystic fibrosis.

Are all genetic changes harmful?

No, not all genetic changes are harmful.

Whist they can sometimes cause problems for our health, this is not always the case.

In fact, genetic changes are responsible for a lot of the differences we see between people. Variation in physical appearance, such as eye colour or skin colour, as well as some behaviours, can be partly accounted for by different genetic changes.

So, do all genetic changes have an effect?

No, the vast majority of genetic changes actually don’t have an observable effect.

We call these changes ‘silent’, and they occur when the change in the DNA sequence does not affect the protein produced.

Is a genetic change the same as a genetic mutation?

Yes, a genetic mutation means the same thing as a genetic change or genetic variant.

Mutation is a term commonly used in scientific literature, however, the negative connotations surrounding this term can be misleading, and might suggest that all genetic changes are harmful.

Because of this, many people in the genetics community now opt to use the term 'variant' instead in scientific and medical literature.

Understanding rare chromosome and gene disorders

Unique is a a charity that aims to provide information and support to anyone affected by rare chromosome or gene disorders.

Founded in 1984, they offer a listening ear for individuals and families who have received a diagnosis, bringing together people from across the world living with rare chromosome or single gene disorders.

13 June is Rare Chromosome Disorder Awareness Day. It is a day to educate and inform those who might not have heard of rare chromosome and gene disorders, and to celebrate all of the unique children and adults and their amazing achievements.

Read more about Unique's Rare Chromosome Disorder Awareness Day.

And finally...

Find out more about Unique on their website.

To read more about how our genes encode our proteins, checkout one of our other blogs, Genomics 101: RNA vs DNA, what's the difference?.

Or, if you found this blog helpful, leave a comment below for more topics you want to see in this Genomics 101 blog series.

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