Some 10.000 years ago, man changed from hunting animals and gathering seeds and tubers in the wild, to keeping animals and growing plants nearby the places where he lived.
In this long process, humans have dramatically changed the animals and plants they originally found in nature. Domesticated cattle, sheep, cats, and dogs are well recognized, but sometimes people are unaware that similar domestication has occurred with many plants we grow as crops, such as maize, wheat, rice, and soybeans. For thousands of years, humans have selected and crossed plants that had characteristics they liked, such as better taste or more yield.
This approach made a huge jump forward when in the 19th century the scientist-monk Gregor Mendel discovered the ‘rules’ by which characteristics were inherited from one generation to the next. Later, scientists discovered that the code for the characteristics of plants, animals and micro-organisms are contained in so called ‘genes’, and that genes consist of genetic material, which we call DNA.
In the early 20th century, plant breeders discovered that mutations in plants do not only occur spontaneously, but can also be induced by exposing plant material to radiation or chemicals.
This has become a widely used technique, and many of the crops we consume every day are obtained with the help of mutations induced by chemicals and radiation.
While cross breeding and induced mutations are and will be extremely important tools of plant breeding, they also have a number of limitations:
- When a gene for a desired trait such as disease resistance is not present in the gene pool of maize for example, then it will not be possible to cross such a gene in from an unrelated species such as wheat;
- For some traits, the genes may be available in the gene pool of, again for example, maize, but those genes are not expressed enough to actually result in the desired trait;
- For some species, such as fruit trees, cross breeding may take decades, which is too long if we need traits that help address the increasing impacts of climate change. For example, it took apple breeders over 50 years to cross resistance against scab, which is a major disease in apple trees that requires many sprays with pesticides per season.
- For other species cross breeding is extremely difficult altogether. Bananas, for example, are sterile and have no seeds. Bananas are multiplied ‘asexually’, which means that to make new banana plants, parts of an existing plant are used. All the resulting bananas are genetically identical.
- The traditional forms of mutation selection by using radiation or chemicals are highly unpredictable and can cause many unintended changes.
- Cross breeding not only brings the desired genes from plant A to plant B (which is usually an ‘elite’ variety that is well adapted to the local environment) but also the tens of thousands other genes of plant A. This so called ‘linkage drag’ forces plant breeders to start a long process of ‘back crossing’.
To overcome these limitations of cross breeding and induced mutation, scientists developed in the 1970s techniques that made it possible to”
- identify a specific gene responsible for a trait in an organism,
- isolate that gene, and
- bring it into plant cells through a process called “transformation”
This process we call ‘genetic modification’, or ‘genetic engineering’ (in the early days of this technology, it was also referred to as ‘recombinant DNA techniques’).