Hi. In this video, we will briefly follow the genetic improvements that have been occurring in agriculture since its existence. The major crops we rely on as our primary food sources were domesticated as crop around 10,000-5,000 years ago. The development of human civilizations is correlated with the development of agriculture, which is one of the most significant achievements in the human history. In the following slide, you can see a map of the world where the main diffusion pathways of humans are represented by black arrows, and the centers of crop domestication by green areas which became permanent settlements. Crops have natural variation within populations and selecting and planting seeds from the best plants increases their representation in subsequent generations, thus improving the crop yield over the time. In many cases, the trait selected weren't the same for different crops, as in the case of cereals such as corn, wheat, barley,or rice. The traits to avoid were; excessive branching, small cob size, hard covers over grains, and scattering of grains, which is that seeds fall off when the plant is harvested. Accumulation of desirable traits and increase of yield arose as a consequence then of cultivation. Mendel and Darwin paved the way for scientific plant breeding. In the early 20 century, the increasing knowledge in genetics stimulated research by improving crop production through cross-pollination, which is the change of genetic material within two plants or by the development of hybrids. The progeny of two genetically different parents often show enhanced growth. This effect is termed hybrid vigor or heterosis. The Green Revolution is the name given to a set of research and technology initiatives occurring between the 50s and 60s that increased agricultural production worldwide. These techniques are a high-yield semi-dwarf grain varieties, expansion of irrigation infrastructure, modernization of management techniques, distribution of hybridized seeds, the production of synthetic fertilizers, and pesticides. So crop productivity kept pace with an increasing growth of population without increasing crop area because of increased yields. More recently, advances in molecular biology have accelerated the science of plant breeding. Maintaining crop production without using more land helps mitigate climate change and slow the loss of biodiversity. Plant scientists can contribute to the alleviation of hunger of a growing world population by developing plants that are drought or stress-resistant, that requires less fertilizer or water, that are resistant to pathogens, and finally by improving their nutrient content. Scientists can afford these goals thanks to the availability of genome sequence data for many important plants. In this slide, you have a list of important plants with their genome sequence data. The genome of an organism is a complete set of DNA, including all of the genes and it is contained in the nucleus of cells in long structures called chromosomes. The molecular structure of DNA was discovered in 1953, thanks to the contribution of the English chemist and X-ray crystallographer, Rosalind Elsie Franklin. Another two important concepts are genotype and phenotype. Genotype is an organism's full hereditary information while phenotype is an organism's actual observed traits such as morphology, development, or behavior. Another important woman of this period was Barbara McClintock, a plant breeder and geneticist. She discovered transposons, the so-called jumping genes because those genes do not exist in a fixed position on a chromosome. For her discovery, she was awarded with a Nobel Prize in 1983. So genome is not a passive system and interacts with the environment. Advances in molecular biology have accelerated science of plant-breeding and there are different model plant-breeding techniques. One of these techniques is the Marker assisted selection (MAS): identifying the location and function of various genes within the genome thanks to DNA markers. For example a disease-resistant trait can be followed through the breeding gene without having to test for disease resistance. Another technique is the double haploids, a genotype formed when haploid cells undergo chromosomes doubling. Our third technique is genome wide-association studies (GWAS). It's a method that allows to identify and select genes associated with complex traits, and finally we have genetic modification, which is adding a specific gene or genes to a plant or knocking down a gene to produce a desirable phenotype. But how can a gene be inserted in the plant genome? We have two basic methods: indirectly by genetic recombination using the bacteria or bacterium mixed with plant cells or directly with the Gene Gun method also called Microinjection or realistic method by injecting particles of DNA with the genetic information into the plant cell chromosomes. Afterwards, cells must be screened for the presence of these transgenes and regenerated to produce a transgenic plant. Mary-Dell Chilton is one of the founders of the modern plant biotechnology. She demonstrate the presence of a fragment of agrobacterium DNA in the nuclear DNA of a crown gall tissue of a plant. In 1983, she led a collaborative research study that produce the first transgenic plant. She received several important awards in recognition of her research. GM plants are transgenic plants and have been developed specifically for pest resistance and herbicide resistance, to use less chemical products usually toxic to the environment, and for producing biofortified foods, like vitamin A, iron and rich in rice or antioxidants and rich in tomatoes for example. GM plants are one of the most divisive topics in society. The concerns about these plants are usually of social, economic, health, or environmental nature. One of these concerns is the risk to human health, including toxicity and allergenicity. Another concern is the risks of evolution of resistance in target pathogens or pests. A third concern is the risks to non-target organisms, so what are called collateral damages. A fourth concern is the risks of gene transfer from crops to weeds and vice versa to weeds to crops because pollen can move DNA between plants. To minimize this possibility, GM plants have to be grown in prescribed distances away from closely-related plants. Finally, we have the risks to take away choice and exploit small farmers. Seeds developed from genetic or transgenic plants must be suited to local conditions and must be affordable for local farmers. So all these issues and concerns are complex and there is a lot of good and bad press about them. Plant biologists can help people to discriminate between fact and fiction about transgenic plants. Scientists need to learn how to communicate more efficiently about this research. We need to harness our knowledge in genetics to breed plants to address global changes, but taking into account all these possible risks that we have been explaining. With this, we've have reached to the end of this video.
