UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes re-edit 11/05/2023 [SEARCH]

2. Changes to the DNA of the genome - what is a mutation? - what are genetic variants?

Doc Brown's Biology exam study revision notes

*

There are various sections to work through, after 1 they can be read and studied in any order.

INDEX of biology notes on genetic variation, and the causes, formation and consequences of mutations

*


(2) Changes can happen to the DNA of the genome - mutations - genetic variants

Sometimes DNA may mutate, meaning a random change occurs in a DNA sequence of an organism.

It is possible for the mutation to be inherited.

This automatically changes the sequence of bases in the DNA molecule.

Therefore the gene expression may be altered or inhibited.

Here we are dealing with a different version of the gene - a genetic variant (also called an allele).

Any mutation changes the sequence of bases in a strand of DNA which produces a different form of the gene (allele), and is called a genetic variant.

In the course of evolution advantageous mutations are more likely to be inherited through successive generations.

All the different versions of genes are called genetic variants or alleles and are formed by mutations (but do not assume they are all harmful to the functioning of an organism!).

diagram of chromosome genes with normal pair of alleles defective alleles gcse biology igcse

Despite the frequency of mutations, most have no or very little effect on the protein synthesised in the ribosomes.

The change in protein structure is usually slight and harmless and its function or appearance is relatively unaffected.

However, certain mutations can have quite an effect on a protein with serious consequences.

This result of this genetic variant may code for a different sequence of amino acids and consequently may change the shape of the final protein structure and its activity.

e.g. theoretically, for an enzyme (protein), its activity may be increased, decreased or completely inhibited its action.

A mutation might even lead to coding for a different amino acid and hence a different protein is produced.

The protein might not be useful or potentially harmful and treated as a 'foreign' substance by the immune system.

If the protein is no longer the right shape it might not be able to perform its function e.g.

(i) an altered shape might mean an enzyme E cannot perform its catalytic action because the substrate molecules S can't lock into the active site - see diagram below (from my Enzymes - structure and functions page).

(ii) If substances like collagen, the main structural protein molecule in the connective tissues of your body, isn't formed properly, muscle tissue can be weakened or completely useless in providing physical support for an organisms body.

Genetic variants can be inherited from one generation to another e.g. mother to child.

See more on the consequences of mutations (on this page)

and  the effects of non-coding DNA (on this page)

and see evolution page for lots more notes on variation


WHAT NEXT?

TOP OF PAGE

INDEX of biology notes on genetic variation, causes, formation and consequences of mutations

INDEX of all my BIOLOGY NOTES

BIG website, try using the [SEARCH BOX], maybe quicker than the many indexes!

UK KS3 Science Quizzes for KS3 science students aged ~11-14, ~US grades 6, 7 and 8

BiologyChemistryPhysics UK GCSE/IGCSE students age ~14-16, ~US grades 9-10

Advanced Level Chemistry for pre-university ~16-18 ~US grades 11-12, K12 Honors

Find your GCSE/IGCSE science course for more help links to all science revision notes

email doc brown - comments - query?

Use your mobile phone or ipad etc. in 'landscape' mode?

Website content Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial.

TOP OF PAGE