6.12 Gregor Mendel

Lived in mid 1800s


  • Experimented with pea plants in garden & studied how traits like height, colour of flowers & colour of pea pods are passed on from one generation to another


Pea plant experiment

  1. Mendel took pea plant with green pods, & pea plant with yellow pods

  2. Crossed plants together & offspring were all yellow pea pods

  3. Took 2 yellow offspring & crossed them together

  4. Offspring were ¾ yellow and ¼ green

  • came up with the term ‘Hereditary units’ which is something passed from one generation to the next

    • the units could be dominant or recessive

    • Recessive is only expressed is the plant got the unit from both parents

  • Offspring in 2nd generation (all yellow) had hereditary units for green pods, but weren’t expressed as they were recessive

  • Green pod in 3rd generation had 2 copies of the recessive hereditary unit, so was expressed


Towards end of 1800s, scientists discovered chromosomes

  • early 1900s, scientists saw similarities between chromosomes and hereditary units

    • hereditary units (genes) were discovered to be on the chromosomes


1950s - double helix DNA structure discovered

2003 - sequenced entire human genome (figured out entire sequence of genetic bases that make up human DNA)