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What
is Genetic Engineering?
A
simple introduction
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 only want to rapidly get an idea of the great difference
between mating and genetic engineering, see the "at a glance" illustration (elementary
level)
Abbreviations:
GE=
Genetically Engineered.
Text difficulty: [EL]
= elemenatry level. [ML]
=
medium level. [AL]
= advanced level.
Contents:
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
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" (this is a simplification,
as explained in "The outdated basis of genetic engineering"
[ML] but it is advisable to read this page first to be able
to grasp that text).
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.
If
you want to know more about DNA, you could look up:
- A
link to a good picture of DNA [ML]
- A
link to a good pedagogical introduction to DNA and genetics
[ML]
- A
link to a good pedagogical introduction to DNA and genetics
2 [ML]
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 string of information in DNA is
divided into pieces called chromosomes. Commonly, each
cell has a double set of chromosomes, one set 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):
A-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-Z
The
corresponding DNA string in the germ cell of the father
(blue):
A-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-Z
(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):
A-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-Z
A-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-Z
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:
o-o-o-o-o-o-o-o-o-o-o-o-o-o-o
(red)
This insertion package is inserted into the DNA of the
recipient organism.
DNA
of the recipient before insertion:
A-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-Z
A-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-Z
(blue)
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:
insertion
package A-o-o-o-o-o-o-o-o-o-o-o-o-o-o-|o-o-o-o-o-o-o-o-o-o-o-o-o-o-o|-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-Z-
A-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-Z
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
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.
Mating:
A-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-Z
A-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-Z
(blue)
Genetic
engineering:
insertion
package A-o-o-o-o-o-o-o-o-o-o-o-o-o-o-|o-o-o-o-o-o-o-o-o-o-o-o-o-o-o|-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-Z-
A-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-Z
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.
Conclusion
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. This is a profound
intervention with unpredictable consequences. |
