nextGenetic Modification (GM) or genetic engineering (GE) is the direct, non-sexual transfer of genetic material to an organism in order to add or change a genetic trait.
Usually genetic traits are transferred to an organism via the process of sexual reproduction - the two gametes from the parents (female egg cell and male pollen) combine to form a zygote (an embryo) that develops into a new individual. GM-technology. In contrast, allows researchers to transfer a very specific piece of DNA (a particular gene or genetic trait) from any other cell to an existing somatic cell and then regenerate a new individual (a GMO) with modified traits from this transformed (genetically modified) cell.
Although breeding is principally based on sexual reproduction other techniques have been used in combination with it to introduce additional genetic variation in crops and production animals.
In mutation breeding chemicals or high-energy radiation is used to induce changes/mutations in the genetic material of organisms, which are then used in a breeding program. According to the FAO (Food & Agriculture Organisation of the United Nations) more than 3 200 varieties of crops bred in this way have been released since the mid-twentieth century, including crops as diverse as ruby grapefruit, rice, sunflowers & pears.
Ploidy refers to the number of sets of chromosomes in a cell. Human gametes (egg cells & sperm) are haploid - containing a single copy of each chromosome or one full set. Consequently, when the two gametes fuse during fertilisation the newly formed embryo and all subsequent somatic cells contain two copies of each chromosome, one from each parent, and are therefore diploid.
Manipulation of the ploidy number during breeding can yield organisms with multiple copies of its genome, e.g. tetraploids (4 copies, for example cotton) and hexaploids (6 copies, for example wheat), with a wide variety of improved traits. Triploid (3 copies) organisms are usually infertile because of their unequal number of chromosomes and have yielded products such as seedless watermelons and bananas.
Hybrid seed development was one of the main contributors to the dramatic increases in agricultural production during the mid-20th century and is based on the cross-pollination of two elite inbred lines to yield highly heterozygous (high degree of genetic variability) individuals/seeds with superior traits.
