production costs through the use of fish with excellent growth properties, a difference that is ultimately reflected in the market price (Liu and Cordes 2004).
The tool traditionally used in breeding was a phenotypic record based on
naked-eye observation of fish phenotypes; this record was subsequently used in
combination with statistical technology to assess genetic capabilities. In theoretical
terms, however, this phenotypic record-based genetic capability assessment
approach was rooted in the idea that innumerable different genes are involved in
specific traits, and each of these genes exhibits the same effects. Genetic capability
assessments in traditional breeding have thus been a matter of evaluating based
solely on phenotypic information, while remaining ignorant about the “black box”
that is the collection of genes actually influencing phenotype.
Recently, rapid advancements in DNA technology have uncovered information
about the chief genes influencing major economically related characteristics. The
various genetic markers developed through DNA technology may actually be
involved in phenotype, but it is arguably the QTLs associated with those markers
that are involved. A genetic map is currently being created for QTL analysis, and
associations with traits in standard line populations are being researched to confirm
the QTLs on the map.
This approach is expected to help in commercialization of new varieties, as it is
possible to use genetic markers as indicators to select the desired genetic treatments,
maintaining only the target genes while also preserving genetic diversity. Selective
breeding with DNA markers is a matter of adding DNA marker information to the
traditional phenotypic record to increase the accuracy of genetic capability
assessments and boost efficiency in genetic improvement (Okamoto 2000).
5.7.2 Selective Breeding with Genetic Markers: An Overview
While DNA markers are being isolated and stockpiled, lines are subjected to linkage
analysis (transmission of two or more allelomorphs together; alleles [genes governing allelomorphic properties] arise because they are located on the same chromosome and do not following independent Mendelian principles in transmission) to
find DNA markers linked to useful genetic properties. If DNA markers linked to such
properties are found, it becomes possible to distinguish the properties through
genotype (using DNA markers) rather than phenotype, allowing for determinations
as to whether the organism possesses that trait (Gjedrem 1983; Okamoto 2000).
A. DNA Markers and Gene Maps
The strategy for learning where genetic traits lie on the genome can be easily
understood if we think of a puzzle. The pieces of the puzzle correspond to DNA
fragments, while the DNA marker is like a symbol showing the characteristics of
the puzzle piece (Fig. 5.14). Hidden in these pieces are genetic traits that are useful
in marine animal breeding, such as those determining fast growth or related to
disease resistance. The proteins or genes determining useful genetic traits are not
5.7 New Marine Breeding with DNA Markers
135
The tool traditionally used in breeding was a phenotypic record based on
naked-eye observation of fish phenotypes; this record was subsequently used in
combination with statistical technology to assess genetic capabilities. In theoretical
terms, however, this phenotypic record-based genetic capability assessment
approach was rooted in the idea that innumerable different genes are involved in
specific traits, and each of these genes exhibits the same effects. Genetic capability
assessments in traditional breeding have thus been a matter of evaluating based
solely on phenotypic information, while remaining ignorant about the “black box”
that is the collection of genes actually influencing phenotype.
Recently, rapid advancements in DNA technology have uncovered information
about the chief genes influencing major economically related characteristics. The
various genetic markers developed through DNA technology may actually be
involved in phenotype, but it is arguably the QTLs associated with those markers
that are involved. A genetic map is currently being created for QTL analysis, and
associations with traits in standard line populations are being researched to confirm
the QTLs on the map.
This approach is expected to help in commercialization of new varieties, as it is
possible to use genetic markers as indicators to select the desired genetic treatments,
maintaining only the target genes while also preserving genetic diversity. Selective
breeding with DNA markers is a matter of adding DNA marker information to the
traditional phenotypic record to increase the accuracy of genetic capability
assessments and boost efficiency in genetic improvement (Okamoto 2000).
5.7.2 Selective Breeding with Genetic Markers: An Overview
While DNA markers are being isolated and stockpiled, lines are subjected to linkage
analysis (transmission of two or more allelomorphs together; alleles [genes governing allelomorphic properties] arise because they are located on the same chromosome and do not following independent Mendelian principles in transmission) to
find DNA markers linked to useful genetic properties. If DNA markers linked to such
properties are found, it becomes possible to distinguish the properties through
genotype (using DNA markers) rather than phenotype, allowing for determinations
as to whether the organism possesses that trait (Gjedrem 1983; Okamoto 2000).
A. DNA Markers and Gene Maps
The strategy for learning where genetic traits lie on the genome can be easily
understood if we think of a puzzle. The pieces of the puzzle correspond to DNA
fragments, while the DNA marker is like a symbol showing the characteristics of
the puzzle piece (Fig. 5.14). Hidden in these pieces are genetic traits that are useful
in marine animal breeding, such as those determining fast growth or related to
disease resistance. The proteins or genes determining useful genetic traits are not
5.7 New Marine Breeding with DNA Markers
135