The understanding of geneticsSpec 4.6.3.3
In short
Gene theory states that characteristics are inherited through genes located on chromosomes. In the mid-19th century, breeding experiments on plants showed that each characteristic is determined by units passed on unchanged. Later, chromosome behaviour during cell division was observed, these units were linked to chromosomes in the early 20th century, and DNA structure was determined in the mid-20th century.
Our current understanding of genetics has developed over time, from the work of many scientists. This led to the gene theory.
| When | What happened |
|---|---|
| Mid-19th century | Gregor Mendel carried out breeding experiments on plants. He observed that the inheritance of each characteristic is determined by 'units' that are passed on to descendants unchanged. |
| Late 19th century | The behaviour of chromosomes during cell division was observed. |
| Early 20th century | It was observed that chromosomes and Mendel's 'units' behaved in similar ways. This led to the idea that the 'units', now called genes, were located on chromosomes. |
| Mid-20th century | The structure of DNA was determined and the mechanism of gene function worked out. |
Why Mendel's work was not recognised until after his death
When Mendel published his results, the behaviour of chromosomes during cell division had not yet been observed. Nobody knew of any structure in cells that his 'units' could be, so there was no way to explain how they were passed on. The link between chromosomes and his 'units' was only made in the early 20th century, after his death. Few scientists read or understood his work at the time.
For 'why was Mendel's work not recognised', the key idea is that chromosomes and their behaviour in cell division had not been observed when he published, so his 'units' could not be linked to any structure in cells.
Written and checked against the AQA GCSE Biology (8461) specification · Updated October 2026