According to the latest reports, 75% of world’s crop has lost their genetic
variations. Explain through the idea of selective breeding why this happened. Also
evaluate the consequences this lose in variation in organisms.
Answers
Specifically, it discusses unexpected outcomes of breeding methods used to develop a food crop or strain and unexpected or unintended effects recorded in the scientific literature. It also includes analyses of methods intentionally used for modifying food sources and comparing the likelihood of unintended changes resulting from the use of genetic engineering versus other methods of genetic modification discussed in Chapter 2.
BACKGROUND
Novel gene combinations arising from the genetic manipulation of existing genes through conventional breeding techniques may introduce unintended and unexpected effects. However, through the breeder's selection process, the genetic lines that express undesirable characteristics are eliminated from further consideration, and only the best lines—those that express desirable characteristics with no additional undesirable agronomic characteristics, such as increased disease susceptibility or poor grain quality—are maintained for possible commercial release. Although plants and animals produced from conventional breeding methods are routinely evaluated for changes in productivity, reproductive efficiency, reactions to disease, and quality characteristics, they are not routinely evaluated for unintended effects at the molecular level. New varieties of food crops, other than those produced using recombinant deoxyribonucleic acid (rDNA) technologies, are rarely subjected to toxicological or other safety assessments (WHO, 2000). Previous National Academies committees have addressed the question of whether unintended effects arising from the use of rDNA-based technologies in food production and the risks potentially associated with them differ in nature and frequency from those associated with non-rDNA-based breeding methods (NRC, 1987, 2000, 2002).
There is a considerable amount of data compiled and available in the scientific literature addressing issues related to genetically modified (GM) and genetically engineered (GE) plants, including health and environmental impacts. In contrast, development of transgenic animals is a relatively new area of biotechnology, and so the amount of data collected and reported for GM animals is less than that for plants. However, the application of genetic modification techniques and the potential for unintended adverse effects are similar for both plants and animals, and much of the information obtained from plants can be applied to questions of concern in the genetic modification of animals.
PLANT BREEDING
Conventional Plant Breeding
Conventional plant production occasionally generates foods with undesirable traits, some of which are potentially hazardous to human health. Most crops naturally produce allergens, toxins, or other antinutritional substances (see Chapter 5). Standard practice among plant breeders and agronomists includes monitoring the levels of potentially hazardous antinutritional substances relevant to the crop. For example, canola breeders monitor levels of glucosinolates in breeding lines under consideration for prospective commercial release, while potato breeders monitor for glycoalkaloid content. If a particular breeding line generates too much of an undesirable substance, that line is eliminated from consideration for commercial release.
In the United States, the plant breeding community is largely self-monitored. Regulatory agencies do not evaluate conventional new crop varieties for health and environmental safety prior to commercial release. Some other countries require government agencies to conduct premarket evaluations for new crop varieties, both conventional and biotechnology-derived. Canada has a “merit system” for the commercial release of new varieties of major field crops, in which candidate varieties are grown in government-administered field trials. Performance data from these trials, related to agronomic factors, disease resistance, and food quality characteristics, are compiled for all candidate and standard commercial varieties. The data are collected from multiple locations over multiple years, as cereal chemists analyze the grain for chemical and nutritional composition and plant pathologists conduct tests to determine reactions to relevant diseases. These data are then evaluated by a team of experts from industry, government, and universities.
The breeder of each candidate variety must convince these experts that it is competitive and worthy relative to other commercially available varieties of that crop, based on the performance data from the trials. Only if the committee agrees is the candidate variety allow