The History of Genetics (OCR GCSE Biology A (Gateway))

The Work of Mendel

• Gregor Mendel was an Austrian monk

• He was studied 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

  • In the first experiment, he crossed a tall pea plant with a dwarf pea plant

  • In the second experiment, he crossed two of the tall offspring together

The pea plant crosses were originally carried out by Mendel to investigate the inheritance of characteristics

• 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)

• He also carried out experiments to show how other characteristics of pea plants are inherited in the same way

  • E.g. Flower colour

Mendel's conclusions

• Three important conclusions about hereditary in plants were reached

  • Characteristics are determined by 'hereditary units' and these hereditary units are passed on from parent to offspring unchanged

  • The offspring receives one 'hereditary unit' from each parent

  • Hereditary units can be dominant or recessive (a dominant characteristic is always expressed when present)

Understanding Mendel's work

• 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)