AQA GCSE Biology

Revision Notes

6.3.3 The Understanding of Genetics

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

Mendel pea plant crosses (1), downloadable IGCSE & GCSE Biology revision notes

  • 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
  • We now know that this is true and call these ‘units’ 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

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