The Understanding of Genetics (AQA GCSE Biology): Revision Note

Mendel's work on genetics

• Gregor Mendel was an Austrian monk

• He was trained in mathematics and natural history at the University of Vienna

• In the mid-19th century, Mendel carried out breeding experiments on plants

• He studied how characteristics were passed on between generations of plants

• For example, he conducted studies with pea plants and looked at how the height characteristic was inherited

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• One of his observations was that the inheritance of each characteristic is determined by ‘units’ that are passed on to descendants unchanged

• Using the example above, Mendel showed that height in pea plants was the result of separately inherited ‘hereditary units’ passed down from each parent plant to the offspring plants – this particular experiment showed that the ‘unit’ for tall plants (T) was dominant over the ‘unit’ for short plants (t)

• His work eventually provided the foundation for modern genetics

• The importance of Mendel’s discovery was not recognised until after his death:

  • His studies were totally new to science in the 19th century

  • There was no knowledge of the mechanisms behind his findings (DNA, genes and chromosomes had not been discovered yet)

Chromosome behaviour

• In the late 19th century and early 20th century, the behaviour of chromosomes during cell division was observed

• Scientists realised that chromosomes behaved in a very similar way to Mendel’s ‘hereditary units’

• Scientists believed Mendel’s ‘units’ must be located on chromosomes

• This is now known to be true and these ‘units’ are called genes

Discovery of DNA structure

• In the mid-20th century (1953 to be precise) the structure of DNA was determined and the mechanism of gene function worked out

• This scientific work by many scientists led to the gene theory being developed