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

Mendel's work on genetics

• Gregor Mendel was an Austrian monk

• 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 to determine how height was inherited

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

• E.g. Mendel showed that the ‘unit’ for tall plants (T) was dominant over the ‘unit’ for short plants (t)

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

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

  • There was no knowledge of the mechanisms behind his findings: the behaviour of chromosomes during cell division, which later made his work make sense, had not yet been observed

  • Other scientists were not aware of his work – it was published in a journal few scientists read

  • Other theories of inheritance (e.g. blending inheritance) were accepted at the time

  • Mendel was a monk, not a well-known or respected scientist, so his work was not taken seriously

  • His work only became important once later discoveries, such as the behaviour of chromosomes during cell division, made it make sense

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 ‘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 the structure of DNA was determined and the mechanism of gene function determined

• This, together with the work of many other scientists, led to gene theory being developed