Gregor MendelSpec 3.11B
In short
In the mid-1800s, a monk breeding pea plants worked out the basis of genetics. He showed that characteristics are passed on as separate inherited factors, one from each parent, now called genes, and that some factors are dominant and others recessive. His work was not understood at the time because genes, DNA and chromosomes were unknown.
Gregor Mendel was a monk who worked out the basis of genetics by breeding pea plants in the mid-1800s. He chose characteristics with clear alternatives, such as tall or short plants, and purple or white flowers.
- He crossed plants with different characteristics and counted the characteristics of the offspring over several generations.
- He found that characteristics are passed on as separate inherited factors, one from each parent. We now call these factors genes.
- He showed that some factors are dominant and others are recessive. For example, crossing pure-breeding tall plants with pure-breeding short plants gave all tall plants. Crossing those offspring with each other gave about three tall plants for every one short plant.
Difficulties before the mechanism was discovered
- Nobody knew about genes, DNA or chromosomes, so there was no mechanism to explain how characteristics are passed on.
- The behaviour of chromosomes during cell division and fertilisation had not been seen, so his ideas could not be linked to anything observable.
- His work was not recognised or understood at the time. It was only appreciated after the structures and processes involved in inheritance were discovered.
Link both halves: Mendel found patterns in how characteristics are inherited, but could not explain them because genes and chromosomes had not yet been discovered.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026