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What is Genetic Engineering?
A simple introduction

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This text is written so that even you who have forgotten much of what you may have learned about genetics will understand it. Therefore, the description is as simple as possible (some details of minor importance have been omitted or simplified).

If you want a very brief overview, go to "A first introduction to genetic engineering".

If you only want to rapidly get an idea of the great difference between mating and genetic engineering, see the "at a glance" illustration (elementary level)

GE= Genetically Engineered.
Text difficulty: [EL] = elemenatry level.   [ML] = medium level.   [AL] = advanced level.


  1. The hereditary substance
  2. Mating - a natural recombination of hereditary information
    1. Mating summarized in a simple illustration
  3. Genetic engineering, an artificial manipulation of genes
    1. Gene insertion summarized in a simple illustration
  4. The difference between mating and genetic engineering at a glance
  5. Genetic engineering is based on an outdated idea
  6. Conclusion

1. The hereditary substance

The hereditary substance, DNA is what is manipulated by Genetic Engineering, below called GE.

DNA contains a complete set of information determining the structure and function of a living organism, be it a bacterium, a plant or a human being. DNA constitutes the genes, which in turn are found in the chromosomes in the cell nucleus.

For schematic picture of the spiral-formed DNA-moleculse click here: DNA

DNA is a very long string of "code words", arranged in an orderly sequence. It contains the instructions for creating all the proteins in the body.

Proteins are truly remarkable molecules. They can have many different properties. All the various tissues in the body are mainly made of proteins. Likewise all kinds of regulatory substances like enzymes, hormones and signal substances. There are many other proteins like for example different substances protecting from infection like antibodies.

The properties of a protein are entirely decided by its form, which is decided by the sequence of its building blocks, the amino acids. The set of code words required to describe one protein is called a "gene"

The DNA-protein system is an ingeniously simple and extremely powerful solution for creating all kinds of biological properties and structures. Just by varying the sequence of code words in the DNA, innumerable variations of proteins with very disparate properties can be obtained, sufficient to generate the enormous variety of biological life. For more about it, see "The cell - a miracle of cooperation" [EL]

If you want to know more about DNA, you could look up:

2. Mating - natural recombination of hereditary information

Through mating, the DNA of two parents is combined.

This can be described in a simplified way like this:

In plants and animals, the DNA is not just one long string of "codewords". It is divided into a set of strings called chromosomes. Commonly, each cell has a double set of chromosomes, one from the mother and one from the father.

In the germinal cells (the cells involved in mating), however, there is just one set. In mating, the set of the mother and father join together to create an embryonic cell with a double set of chromosomes. This embryonic cell divides into two identical copies. These divide in turn. In this way the whole organism will come to contain identical sets of chromosomes (the reason that the tissues have different properties in different parts of the grown up body is that different genes are active in them).

Mating summarized in a simple illustration

(The DNA of plants and animals contains hundreds of millions of "code syllables". To represent the complete set of information, each circle below would correspond to about 30 million code syllables. In the illustration below, each circle represents 300 code syllables. One code word, corresponding to one amino acid, contains three code syllables. One gene contains at an average about 1000 code words. The genes are about 3% of all DNA)

(The names of the colors have been written to simplify for those with color blindness)

A DNA string (part of a chromosome) in the germ cell of the mother (green):

The corresponding DNA string in the germ cell of the father (blue) :

(The syllables A and Z are just symbolical to mark the beginning and end of the two corresponding DNA strings).

Through mating, the strings are combined to create the DNA of the body cells:

The combined DNA in the offspring (one green and one blue string):

So in mating, there occurs no manipulation of the natural and orderly sequence of code words and sets of code words, the genes.

3. Genetic engineering, an artificial manipulation of genes

In genetic engineering, one gene or most commonly, a set of a few genes is taken out of the DNA of one organism and inserted into the DNA of another organism. This we call the "insertion package" illustrated in red:

Insertion package (red):


This insertion package is inserted into the DNA of the recipient organism.

DNA of the recipient before insertion:

There is no way to make a gene insert in a predetermined location. So the insertion is completely haphazard. Below the insertion package (red) has happened to become inserted in the chromosome string stemming from the mother (green):

DNA of the recipient after insertion:

This means that the sequential order of the genetic code of the mother string has been disrupted by a sequence of codes that are completely out of place. This may have several serious consequences as you find more about in "Is Genetic Engineering a variety of breeding?"[ML].

4. The difference between mating and genetic engineering at a glance

A. First important difference

In mating a chromosome from the mother, o-o-o-o (green ) is combined with a chromosome of the father, o-o-o-o (blue). The sequence of DNA "code words" in each chromosome remains unchanged. And the chromosomes remain stable. The mating mechanism has been developed over billions of years and yields stable and reliable results.


Genetic engineering:

In genetic engineering, a set of foreign genes, o-o-o-o (red) is inserted haphazardly in the midst of the sequence of DNA "code words" (in this case in the DNA inherited from the mother [green])). The insertion disrupts the ordinary command code sequence in the DNA. This disruption may disturb the functioning of the cell in unpredictable and potentially hazardous ways. The insertion may make the chromosome unstable in an unpredictable way.

B. Second important difference

A second fundamental difference is that, in genetic engineering, special constructs of genetic material derived from viruses and bacteria are added to the "desired gene". These constructs don't exist in natural food. They are needed for three major purposes:

  1. To detect cases of successful gene insertion (markers)
  2. To ensure that the inserted gene is not rejected by the recipient organism (vectors)
  3. To ensure that the inserted gene is active (promoters)

These constructs may cause trouble of various kinds. See e.g.:

For more about how these constructs work, see: "How are genes engineered" [ML] Explains the technique of Genetic Engineering.

5. Genetic engineering is based on an outdated idea

The key assumption of genetic engineering is that you can "tailor" organisms by adding genes with desirable properties. But science has found that genes don't work as isolated carriers of properties. Instead the effects of every gene is the outcome of interaction with its environment. The situation is succinctly summarized by Dr Craig Venter:

"In everyday language the talk is about a gene for this and a gene for that. We are now finding that that is rarely so. The number of genes that work in that way can almost be counted on your fingers, because we are just not hard-wired in that way."

"You cannot define the function of genes without defining the influence of the environment. The notion that one gene equals one disease, or that one gene produces one key protein, is flying out of the window."

Dr. J. Craig Venter, Time's Scientist of the year (2000). President of the Celera Corporation. Dr. Venter is recognized as one of the two most important scientists in the worldwide effort to map the human genome.

Source: Times, Monday February 12, 2001 "Why you can't judge a man by his genes",,2-82213,00.html

This is further explained in "The new understanding of genes"  [ML].


So technically, genetic engineering is an unnatural insertion of a foreign sequence of genetic codes in the midst of the orderly sequence of genetic codes of the recipient, developed through millions of years. In addition, powerful artificial genetic constructs are added with potentially problematic effects. This is a profound intervention with unpredictable consequences:

"Up to now, living organisms have evolved very slowly, and new forms have had plenty of time to settle in. Now whole proteins will be transposed overnight into wholly new associations, with consequences no one can foretell, either for the host organism, or their neighbors.... going ahead in this direction may be not only unwise, but dangerous. Potentially, it could breed new animal and plant diseases, new sources of cancer, novel epidemics."

Dr. George Wald. Nobel Laureate in Medicine 1967. Higgins Professor of Biology, Harvard University.
(From: 'The Case against Genetic Engineering' by George Wald, in The Recombinant DNA Debate, Jackson and Stich, Eds. P. 127-128. ; Reprinted from The Sciences, Sept./Oct. 1976 issue)

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