In contrast, countries in Africa and elsewhere in Asia are still faced with a severe
shortage of animal protein resources. Many of these regions have vast inland waters
or ocean areas that go almost entirely unused. It would not be an overstatement to
say that achieving a revolutionary increase in food self-sufficiency hinges on
advancements in fish and shellfish aquaculture. One means of addressing this would
be through the breeding of species that can be cultivated easily and are capable of
withstanding particular environmental conditions, such as local water temperature
and quality and salt concentrations.
In that sense, the specific goals of fisheries breeding—its aims and the fish
involved—have changed with the times even as general interest in fisheries
breeding has grown. For instance, while it was once thought that fast-growing lines
were better, recent examples involving color carp and whales have actually required
dwarf lines that do not grow. Even when the goal is to produce tasty fish for eating,
the genetic characteristics demanded of the fish vary according to how it is eaten.
For this reason, researchers involved in fish breeding must make active use of
biotechnology to accelerate breeding methods.
4.2 Chromosome Manipulation
Chromosome manipulation techniques originated in agriculture with the use of
varieties with naturally or artificially modified chromosome numbers for breeding
(i.e., the creation of superior or improved varieties through hybridization). Typically,
organisms that engage in sexual reproduction (reproduction in which organisms are
sexually specialized into female and male forms) are diploid (2n), meaning that they
possess pairs of identical chromosomes. Humans possess 46 chromosomes, or 23
pairs (2n = 46). One comes from the maternal line by way of the egg, while the other
comes from the paternal line via the sperm. When the number of chromosomes is
altered, however, the result is a new, never-before-seen organism. This manipulation
of chromosomes to create new organisms is known as chromosome set manipulation.
Chromosome set manipulation is widely used today, as it not only can be performed
through simple methods but has the advantage of not requiring special or expensive
equipment (Vorobjev et al. 1993; Arai 2001; Endo 2007).
For improvement of varieties through chromosome manipulation, polyploids are
typically used. As mentioned previously, an organism’s chromosomes exist in
diploid (2n) form, with one gene each received from the mother and father. Some
organisms, however, exist in quadruploid (4n) or sextuploid (6n) form, with their
number of chromosomes doubled or tripled; others are haploid (n), meaning that they
have only half the number of chromosomes. The term “polyploid” refers to organisms with multiples of the number of chromosomes, while “polyploidy” refers to the
state in which polyploids exist. Autopolyploids are organisms that have three or more
of the same genome (chromosome pairs). The term “aneuploidy” describes cases in
which part of the chromosome is lost, such as 2 n + 1 or 2 n − 1 (Oshiro 1990).
4.1 The Global Food Shortage and Genetic Engineering
81
shortage of animal protein resources. Many of these regions have vast inland waters
or ocean areas that go almost entirely unused. It would not be an overstatement to
say that achieving a revolutionary increase in food self-sufficiency hinges on
advancements in fish and shellfish aquaculture. One means of addressing this would
be through the breeding of species that can be cultivated easily and are capable of
withstanding particular environmental conditions, such as local water temperature
and quality and salt concentrations.
In that sense, the specific goals of fisheries breeding—its aims and the fish
involved—have changed with the times even as general interest in fisheries
breeding has grown. For instance, while it was once thought that fast-growing lines
were better, recent examples involving color carp and whales have actually required
dwarf lines that do not grow. Even when the goal is to produce tasty fish for eating,
the genetic characteristics demanded of the fish vary according to how it is eaten.
For this reason, researchers involved in fish breeding must make active use of
biotechnology to accelerate breeding methods.
4.2 Chromosome Manipulation
Chromosome manipulation techniques originated in agriculture with the use of
varieties with naturally or artificially modified chromosome numbers for breeding
(i.e., the creation of superior or improved varieties through hybridization). Typically,
organisms that engage in sexual reproduction (reproduction in which organisms are
sexually specialized into female and male forms) are diploid (2n), meaning that they
possess pairs of identical chromosomes. Humans possess 46 chromosomes, or 23
pairs (2n = 46). One comes from the maternal line by way of the egg, while the other
comes from the paternal line via the sperm. When the number of chromosomes is
altered, however, the result is a new, never-before-seen organism. This manipulation
of chromosomes to create new organisms is known as chromosome set manipulation.
Chromosome set manipulation is widely used today, as it not only can be performed
through simple methods but has the advantage of not requiring special or expensive
equipment (Vorobjev et al. 1993; Arai 2001; Endo 2007).
For improvement of varieties through chromosome manipulation, polyploids are
typically used. As mentioned previously, an organism’s chromosomes exist in
diploid (2n) form, with one gene each received from the mother and father. Some
organisms, however, exist in quadruploid (4n) or sextuploid (6n) form, with their
number of chromosomes doubled or tripled; others are haploid (n), meaning that they
have only half the number of chromosomes. The term “polyploid” refers to organisms with multiples of the number of chromosomes, while “polyploidy” refers to the
state in which polyploids exist. Autopolyploids are organisms that have three or more
of the same genome (chromosome pairs). The term “aneuploidy” describes cases in
which part of the chromosome is lost, such as 2 n + 1 or 2 n − 1 (Oshiro 1990).
4.1 The Global Food Shortage and Genetic Engineering
81