are expected to be discovered and studied through the biological world, these too
will be introduced and applied to breeding across species boundaries.
4.4.1 Basic Techniques
Genes were first understood as hypothetical particles, proposed by Mendel in 1865
to explain genetic phenomena and their principles. Today, molecular genetics and
genetic engineering have achieved rapid advancements, and it has become possible
for to actually obtain genes and to improve and use them freely.
As noted previously, genes are large molecules within the double helix structure
of DNA, which exist in the same form in all somatic cell nuclei. As is widely
known, a single gene, depending on the sequence of bases that compose it, designates and possesses a diagram for the structure of specific proteins and RNA
produced by the cell.
Within chromosomal DNA, genes are located at specific intervals. They may be
understood as similar to stations on a railway or oases in a desert. Internally, genes
have a complex structure; the portions that are finally translated into proteins are
dispersed and are known as expressed sites (structure sequences), while the
untranslated portions between the expression sites are known as non-expressed sites
(intervening sequences). Within the nucleus, all information—including both types
—is transcribed to RNA, after which only the expressed sites, and not the
non-expressed sites, are spliced together to form messenger RNA (mRNA). This
mRNA is then transported to the cytoplasm and translated into proteins. A single
complete gene also includes a portion known as an enhancer, a promoter gene that
is actually transcribed and is necessary for expression to take place (Fig. 4.10).
Fish breeding may be conceived as consisting of two stages: modification of the
gene to be introduced and introduction of the gene to the egg cell. The following
section explains the basic techniques needed for each stage.
A. Modification of Foreign Genes
1. Separation
Following removal of proteins from the tissue extract with enzymes and phenol,
the nucleic acid (DNA and RNA) is precipitated with alcohol. The RNA may be
removed with enzymes to obtain DNA. mRNA may be separated into specific end
sequences (poly(A)) through chromatography (Williams et al. 1991).
2. Dissociation and Truncation
Dissociation and recombination of the DNA double helix can be performed
easily through acid and base treatment. Various enzymes are used as “scissors” to
cut the nucleic acid chain itself. These enzymes include DNase (or RNase), which
truncate whatever DNA (or RNA) they come across, and a number of restriction
4.4 Gene Manipulation
97
will be introduced and applied to breeding across species boundaries.
4.4.1 Basic Techniques
Genes were first understood as hypothetical particles, proposed by Mendel in 1865
to explain genetic phenomena and their principles. Today, molecular genetics and
genetic engineering have achieved rapid advancements, and it has become possible
for to actually obtain genes and to improve and use them freely.
As noted previously, genes are large molecules within the double helix structure
of DNA, which exist in the same form in all somatic cell nuclei. As is widely
known, a single gene, depending on the sequence of bases that compose it, designates and possesses a diagram for the structure of specific proteins and RNA
produced by the cell.
Within chromosomal DNA, genes are located at specific intervals. They may be
understood as similar to stations on a railway or oases in a desert. Internally, genes
have a complex structure; the portions that are finally translated into proteins are
dispersed and are known as expressed sites (structure sequences), while the
untranslated portions between the expression sites are known as non-expressed sites
(intervening sequences). Within the nucleus, all information—including both types
—is transcribed to RNA, after which only the expressed sites, and not the
non-expressed sites, are spliced together to form messenger RNA (mRNA). This
mRNA is then transported to the cytoplasm and translated into proteins. A single
complete gene also includes a portion known as an enhancer, a promoter gene that
is actually transcribed and is necessary for expression to take place (Fig. 4.10).
Fish breeding may be conceived as consisting of two stages: modification of the
gene to be introduced and introduction of the gene to the egg cell. The following
section explains the basic techniques needed for each stage.
A. Modification of Foreign Genes
1. Separation
Following removal of proteins from the tissue extract with enzymes and phenol,
the nucleic acid (DNA and RNA) is precipitated with alcohol. The RNA may be
removed with enzymes to obtain DNA. mRNA may be separated into specific end
sequences (poly(A)) through chromatography (Williams et al. 1991).
2. Dissociation and Truncation
Dissociation and recombination of the DNA double helix can be performed
easily through acid and base treatment. Various enzymes are used as “scissors” to
cut the nucleic acid chain itself. These enzymes include DNase (or RNase), which
truncate whatever DNA (or RNA) they come across, and a number of restriction
4.4 Gene Manipulation
97