6.3.3: The understanding of genetics (biology only)
Not started yet — this one needs some love.
In the mid-19th century Gregor Mendel carried out breeding experiments on plants.
Mendel observed that the inheritance of each characteristic is determined by “units” that are passed on to descendants unchanged.
In the late 19th century, behaviour of chromosomes during cell division was observed.
In the early 20th century, chromosomes and Mendel’s “units” were observed to behave in similar ways.
This led to the idea that Mendel’s “units”, now called genes, were located on chromosomes.
In the mid-20th century the structure of DNA was determined and the mechanism of gene function worked out.
Scientific work by many scientists led to the gene theory being developed.
Mendel’s discovery was not recognised until after his death because chromosomes, DNA structure and gene function were not yet understood.
Common exam mistakes
Do not treat Mendel’s work as accepted immediately; it was recognised later when chromosomes, DNA and genes were better understood.
Mendel’s "units" of inheritance are now called genes, not chromosomes.
Link the chromosome evidence to genes by saying chromosomes and Mendel’s units behaved in similar ways.
The gene theory developed from work by many scientists, not one discovery alone.