Genetic Modification in Nature
Prof. C Kameswara Rao
Foundation for Biotechnology Awareness and Education, Bangalore, India
www.fbae.org; firstname.lastname@example.org, http://fbae.blogs.com/
GM, GMO, LMO:
The terms ‘Genetic Modification (GM)’, ‘Genetically Modified Organisms (GMO)’ and ‘Living Modified Organisms (LMO)’, are used indiscriminately in the context of modern biotechnology. In reality, these terms not only accurately apply to all wild organisms and cultivated plants and domesticated animals of classical agriculture and animal husbandry, but also constitute an imprecise terminology for the products of modern biotechnology, involving Genetic Engineering (GE).
The term Biotechnology, coined by Karl Ereky in 1919, is the short form of biological technology, referring to the large or industrial scale use of organisms, their components (proteins, DNA) or secondary metabolites (natural products).
Biotechnology is over 6,000 years old, as exemplified by the age-old products of day-to-day use such as wine, vinegar, bread, cheese, fermented foods and the organisms that produce them. The conventional industrial production of enzymes, antibiotics, vaccines and antibodies is also biotechnology.
Modern biotechnology uses refined concepts and sophisticated techniques for genetic modification, aimed at providing improved products such as transgenic organisms or DNA vaccines, or services such as managing environmental pollution through bioremediation.
Genetic modification in nature:
All the existing wild species of plants and animals are the result of genetic modification by nature. In nature, traits with an adaptive value, i.e., traits advantageous for the survival of the species, have continuously been preserved by Natural Selection. Natural Selection results in genetic modification, and in turn in new varieties and species. Natural Selection cannot cause new genetic variation, but only operates at a given time, upon the existing variation in the genes for different traits in a population
Natural sources of genetic variation:
a) Gene mutations: Whenever a cell undergoes division, mitosis in the body cells or meiosis in the sexual cells, new copies of the entire DNA in the cell are made. This is DNA replication, which uses both the strands of the DNA in the cell as templates. This process is very faithful, but occasionally some copying errors creep in, resulting in a different sequence of nucleotides, which means changed (mutated) genes. Since there are several copies of the same gene, many mutations do not initially matter and they do not also matter when not affecting important metabolic processes. Mutations with an adaptive value to the population/species are fixed in the population by Natural Selection. If a mutation is deleterious, the individuals containing it as well as the mutated gene are eliminated. Mutations that have neither beneficial nor deleterious effects at the time remain dormant in the population (neutral mutations), till the environmental forces tilt the balance making them either beneficial or deleterious.
Mutations occur routinely in nature and have been responsible for an enormous number of new varieties and species. The population with selected mutations is genetically modified, and will be different from the parents. This is how most of biological evolution progresses, but extremely slowly, requiring a large number of generations for perceptible changes to establish.
b) Gene flow: A fair degree of genetic modification occurs through gene flow or gene migration, which is the transfer of genes from one population of a species to another of the same species, during sexual reproduction, followed by Natural Selection.
c) Natural hybridization: A hybrid is the offspring of two varieties (intervarietal), species (interspecific) or genera (intergeneric). In nature, the identity of species is protected through reproductive isolation operating through reproductive barriers, which may be genetical, physiological, geographical, temporal or even physical factors. Reproductively isolated species cannot exchange genes, and such populations/species breed only among themselves producing fertile offspring. Natural hybridization occurs fairly frequently since reproductive isolation is lax to different degrees in several species. Though unstable initially, hybrid progenies are often more vigorous on account of a phenomenon called hybrid vigour or heterosis, and so are more successful than either parent. Natural intervarietal, interspecific or intergeneric hybridization occurred all the time producing several thousand new hybrid species.
While genetic modification through mutations and gene flow is a slow process, genetic modification through hybridization is sudden, leading to a new species from one generation to the immediate next.
d) Change in the chromosome number: All organisms have a fixed number of chromosomes and most organisms have two sets of chromosomes (diploids) in their body cells. Species/varieties with three (triploids), four (tetraploids) or more sets of chromosomes, commonly occur in nature. Populations with such multiple sets of chromosomes are polyploids.
Several wild species have chromosomes in numbers differing from the ancestral species, but not in multiple sets. These are aneuploids, which have lost or duplicated one or more chromosomes.
e) Chromosomal aberrations:In some species individual chromosomes undergo physical structural rearrangements, exchanging segments within or between chromosomes of a cell, affecting the positions and expression of genes in those segments.
Polyploids, aneuploids and chromosomal aberrant species are reproductively unstable and worse when they hybridize. Their fertility is restored if each of the different sets of chromosomes is duplicated. Such species are amphidiploids and several occur in nature.
Modified gene expression:
Variation in the chromosome number or structure causes variation in the number of sets of genes or their position, and both modify gene expression, making such populations different from the parental species.
November 19, 2005