become amenable to mass production are few and far between. Reasons for this
include the short timespan over which mass production of marine organisms
through farming has been possible, as well as the concentration of efforts to date on
achieving stable quantitative production. Consumers today are demanding qualitative improvements to farmed fish, in the hopes of enjoying safer and more delicious farmed fish that is also amenable to stable mass production.
Qualitative improvements are achieved through breeding (strain improvements),
which in turn is made possible through an understanding of genetic character. As
noted in the previous section, genome research at the molecular level has resulted in
many achievements in terms of genetic information. One of these that may be
described as historic in its implications is the method known as quantitative trait
locus (QLT) analysis, in which DNA markers can be used to explore as yet
unknown gene loci that govern or are connected with phenotype. While QLT
analysis is ultimately a matter of using positional cloning to locate responsible
genes, the discovery of DNA markers associated with phenotype would also enable
their use in breeding.
This method stands to increase efficiency to an unimaginable degree in breeding
that has previously been reliant solely on phenotypes. It is the subject of great
attention in modern science, where the new breeding approach is referred to as
marker assisted selection (MAS). In terms of use of genetic information, two
approaches exist. One is the so-called “hard path,” which involves actively
manipulating genes to alter organisms and artificially produce useful materials for
application in production or treatment. The other is the “soft path,” which involves
using genetic information to take maximum advantage of organisms’ genetic
capabilities without actually manipulating their genes. Selective breeding through
genetic markers falls into this category: because the fish’s genetic information can
used when selecting parents, allowing for selection through recombination, greater
efficiency can be achieved than in current selective breeding, where parents have
been selected based on phenotypic information. In terms of breeding methods,
MAS is no different from current statistically based selected breeding, but the
genetic information involved in economically related traits can provide a means of
precisely selecting genetically superior organisms (Okamoto 2000).
5.7.1 Reasons for Using Genetic Marker Selective Breeding
in Marine Fisheries Products
As noted previously, the achievement of stable quantitative production of farmed
fish has led consumers in the contemporary environment of widespread farmed fish
use to demand safer and more delicious seafood. Producers of farmed fish similarly
would like to create varieties that meet these consumer demands. By using fish
species that are resistant to disease and can adapt readily to temperature changes,
they can reduce the incidence of disease and farm without the use of medicines or
antibiotics, allowing them to meet consumer demand for safe food products.
Consumer demands can also be met with high-quality fish and reductions in
134
5 Genetic Diversity and DNA Markers in Fish
include the short timespan over which mass production of marine organisms
through farming has been possible, as well as the concentration of efforts to date on
achieving stable quantitative production. Consumers today are demanding qualitative improvements to farmed fish, in the hopes of enjoying safer and more delicious farmed fish that is also amenable to stable mass production.
Qualitative improvements are achieved through breeding (strain improvements),
which in turn is made possible through an understanding of genetic character. As
noted in the previous section, genome research at the molecular level has resulted in
many achievements in terms of genetic information. One of these that may be
described as historic in its implications is the method known as quantitative trait
locus (QLT) analysis, in which DNA markers can be used to explore as yet
unknown gene loci that govern or are connected with phenotype. While QLT
analysis is ultimately a matter of using positional cloning to locate responsible
genes, the discovery of DNA markers associated with phenotype would also enable
their use in breeding.
This method stands to increase efficiency to an unimaginable degree in breeding
that has previously been reliant solely on phenotypes. It is the subject of great
attention in modern science, where the new breeding approach is referred to as
marker assisted selection (MAS). In terms of use of genetic information, two
approaches exist. One is the so-called “hard path,” which involves actively
manipulating genes to alter organisms and artificially produce useful materials for
application in production or treatment. The other is the “soft path,” which involves
using genetic information to take maximum advantage of organisms’ genetic
capabilities without actually manipulating their genes. Selective breeding through
genetic markers falls into this category: because the fish’s genetic information can
used when selecting parents, allowing for selection through recombination, greater
efficiency can be achieved than in current selective breeding, where parents have
been selected based on phenotypic information. In terms of breeding methods,
MAS is no different from current statistically based selected breeding, but the
genetic information involved in economically related traits can provide a means of
precisely selecting genetically superior organisms (Okamoto 2000).
5.7.1 Reasons for Using Genetic Marker Selective Breeding
in Marine Fisheries Products
As noted previously, the achievement of stable quantitative production of farmed
fish has led consumers in the contemporary environment of widespread farmed fish
use to demand safer and more delicious seafood. Producers of farmed fish similarly
would like to create varieties that meet these consumer demands. By using fish
species that are resistant to disease and can adapt readily to temperature changes,
they can reduce the incidence of disease and farm without the use of medicines or
antibiotics, allowing them to meet consumer demand for safe food products.
Consumer demands can also be met with high-quality fish and reductions in
134
5 Genetic Diversity and DNA Markers in Fish