What are genes and gene variants?

Our bodies are made up of tiny building blocks called cells. Inside nearly every cell is a set of genes. Genes are the instructions for your body to work.

If a gene is changed, it may not give the correct instructions anymore. A change in a gene is called a genetic variant or gene mutation.

Over time, genetic variants in a cell may stop the cell working normally. Cancer may develop if cells like this multiply in an abnormal way and grow out of control.

What is an acquired variant?

An acquired variant is a gene change that happens during a person's lifetime. This is also called a somatic gene variant.

Acquired variants may happen:

  • by chance, when a cell divides or does its job in the body
  • because of lifestyle – for example, diet or physical activity levels
  • because of things in a person's environment – for example, sunlight or tobacco smoke.

This type of gene change only affects certain cells in the person’s body. It cannot be passed from a parent to child (inherited). A cancer may develop where there are cells with acquired variants. For example, if genes in lung cells are damaged because of smoking, this may eventually allow lung cancer to develop.

What is an inherited variant?

A gene change that is passed from parent to child is called an inherited variant or mutation. This type of gene change is there from birth. It is in almost every cell in the person’s body for their whole life.

Some inherited gene variants cause a higher risk of certain types of cancer. The gene variant by itself does not cause cancer. But it may allow other damage to build up faster in cells. This increases the chance that cancer will develop.

How are genes inherited from parents?

Genes are passed from parent to child (inherited) when a sperm and egg join to start a pregnancy (conception).

Each person has 2 copies of each gene. One is from our mother and the other from our father:

  • The sperm contains 1 copy of the father’s genes.
  • The egg contains 1 copy of the mother’s genes.

You only get 1 copy of each of your parent’s genes. If one parent has a gene variant, you either get the copy with the variant or the copy without the variant.

This means there is a 1 in 2 (50%) chance the gene variant is passed on.

How genes are inherited

Parent and child figures are used to show how 4 combinations of genes can be made from 1 sperm and 1 egg. 2 of the combinations contain a gene variant carried by 1 parent.
Image: The image shows a female and male figure. A pair of genes is shown beside each figure. The female has two green genes shown side by side. The male figure has a green gene and a red gene shown side by side. The red gene is the gene variant. Below the female, two circles are shown. These are two eggs. Each egg contains a copy of one of the female’s genes. Below the male, two ovals with tails are shown. These are two sperm. Each sperm contains a copy of one of the male’s genes. One sperm contains the green gene. The other sperm contains the red gene variant. Lines travel down from each egg and sperm to four child figures. The lines show which genes have passed from an egg and a sperm to each child. Four possible combinations of genes can be made using one of the eggs and one of the sperm. Two of the children have two green genes. They have a copy of a green gene from one of the eggs and a copy of the green gene from the sperm. Two children have a green gene and a red gene variant. They have a copy of a green gene from one of the eggs and a copy of the red gene variant from the other sperm.

If you have the gene variant, there is a 1 in 2 (50%) chance any children you have will inherit it.

Can cancer genes skip a generation?

Cancer gene variants cannot skip or miss a generation. If one of your parents has a gene variant, there is a 1 in 2 (50%) chance it has passed to you. You either inherit it or you do not. If you do not inherit the variant, you cannot pass it to your children.

Sometimes it can seem like the cancer skipped a generation. This is usually because a person in the family has the variant which is then passed on to their child. But the person does not develop cancer themselves.

This might happen because of the following reasons:

  • Having a cancer gene variant raises a person’s risk of developing cancer. But it does not mean they will definitely develop cancer. Sometimes the person does not develop cancer, but their child inherits the variant and does. This can seem like the cancer gene has skipped a generation.
  • A person may inherit and pass on a cancer gene variant for a cancer type they cannot develop themselves. For example, gene variants linked to breast and ovarian cancers can pass through the father’s side of the family. A father who inherits this type of variant is unlikely to develop breast cancer and cannot develop ovarian cancer. But they still have a 1 in 2 (50%) chance of passing the variant to their children. If their daughter inherits the variant and develops breast or ovarian cancer, it can seem like the cancer gene has skipped a generation.

More information about cancer and genes

If you are worried you may have inherited a cancer gene variant, our information about family history, genes and cancer risk may help. It explains:

  • how information about your family history can be used to assess your risk of cancer
  • ways to reduce and manage inherited cancer risk
  • more about some genetic conditions and inherited cancer syndromes.

We also have information about how the genes in cancer cells can be used to develop or plan cancer treatment. Find out more about:

About our information

  • References

    Below is a sample of the sources used in our family history and cancer information. If you would like more information about the sources we use, please contact us at  cancerinformationteam@macmillan.org.uk

    Monahan KJ, Bradshaw N, Dolwani S, et al. Guidelines for the management of hereditary colorectal cancer from the British Society of Gastroenterology (BSG)/Association of Coloproctology of Great Britain and Ireland (ACPGBI)/United Kingdom Cancer Genetics Group (UKCGG). Gut. 2020; 69: 411–444. Available from DOI: 10.1136/gutjnl-2019-319915 (accessed October 2022).

    NICE. Familial breast cancer: classification, care and managing breast cancer and related risks in people with a family history of breast cancer. Clinical guideline [CG164]. Last updated: 20 November 2019. Available from https://www.nice.org.uk/guidance/CG164 (accessed October 2022).

    NICE. Molecular testing strategies for Lynch syndrome in people with colorectal cancer. Diagnostics guidance [DG27]. Published: 22 February 2017. Available from https://www.nice.org.uk/guidance/dg27 (accessed October 2022).

    NICE. Testing strategies for Lynch syndrome in people with endometrial cancer. Diagnostics guidance [DG42]. Published: 28 October 2020. Available from https://www.nice.org.uk/guidance/dg42 (accessed October 2022).

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Marc Tischkowitz, Reader and Honorary Consultant Physician in Medical Genetics.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 October 2022
Next review: 01 October 2025
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.