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Mutated genes

Genes where the sequence of DNA has changed

Mutation

A change in the arrangement or amount of genetic material in a cell.

Bases

Bases, sometimes called nitrogenous bases, are the parts of the DNA molecule that join the two helix strands. They are like rungs on a ladder. There are four bases: adenine (A), thymine (T), guanine (G) and cytosine (C). Each base can only join with one other base; i.e. they join together in pairs: A with T and G with C.

Gene mutations and cancer

The information in DNA is carried in the sequence of bases. Changes, or mutations, in just one or two bases can scramble the information and mean that the gene does not work properly. If this mutation is in a gene that controls cell division it can trigger the uncontrolled replication of that cell. This faulty gene is copied to all the new cells and so the uncontrolled growth continues. The cells form a tumour.

A gene

Only a few bases have to change to cause a mutation in a gene.

Genes and DNA

To find out more about DNA, genes and mutations click on the links:

Genes and DNA

Gene mutations

Researchers are starting to understand the genetic basis of many cancers. This allows improvements in diagnosis, medicines and treatments. It is even becoming possible to see which people may be more likely to develop certain types of cancers.

Cancers linked to known genetic markers

Cancer is quite rare, especially in people under the age of 60. However, some cancers appear to 'run in families'. Researchers have found that certain mutated genes, passed from parents to their children, can dramatically increase the chance of developing a particular cancer. Inheriting the faulty gene does not guarantee that the person will develop cancer but it appears to increase the chance that they will.

Genetic tests can be made to see if a person has inherited a mutated gene that makes them more likely to develop cancer. Some genes, such as P53, are associated with a range of types of cancer, others are specific to just one type.

Cancer Examples of genes associated with specific cancers:
Breast cancer BRCA1, BRCA2
Ovarian cancer BRCA1, BRCA2
Prostate cancer BRCA2, HPC1, HPC2, HPCX
Melanoma (skin cancer) CDKN2A, MITF
Stomach CDH1 (E-cadherin)
Bowel cancer MSH2, MSH6, MLH1, APC

Using the information

There are ethical issues around genetic screening. The results can tell a person if they are at a higher than normal risk of developing cancer, but what should be done with this information?

Would you want to know that you were at high risk? What would you do if you did know? How would you react if you were clear of any mutated genes? How should doctors handle this information? Should doctors screen for cancers that cannot be cured?

What decisions would you make? How would you help someone thinking about having a genetic test decide what to do?

For more on the ethical questions relating to inherited disorders, see the Human Genome Project resource.

Question 4

Quiz Print
a)
What are the benefits of genetic screening for cancer?

  • Knowing the risk of developing cancer
  • Knowing if anything could be passed on to your children
  • Being able to make life-decisions knowing the risk of developing cancer
  • Being able to monitor for cancer more closely
b)
What are the disadvantages of genetic screening for cancer?

  • May not give a definite answer - only suggest the risk of developing cancer
  • Knowing the risks could be stressful and cause other problems
  • What happens if there is no cure or treatment for the cancer?
  • What do you say to close friends and family?
  • How will it influence your life-decisions?