repeated inbreeding results in the positions of all genes approximating a homozygotic organism. At the same time, a group of clones is achieved in which all
organisms are nearly identical genetically. Homozygotic clones are referred to as a
“pure line.” Several repetitions of gynogenesis were expected to result in establishment of a pure line in the generation faster than with inbreeding. If no crossing
occurs at all between homologous chromosomes at a synapsis during maturation
division, blocking of second polar body emission to form a gynogenetic diploid
results in the position of heterosynaptic genes becoming homosynaptic, producing
an organism that is homosynaptic for all genetic positions (homosynaptic
organism).
For the second gynogenetic generation from these female parents, homosynaptic
groups (clones) appear that always have the same genes at the same gene locations.
Indeed, crossing occurs between homologous chromosomes, and the position of
hetero genes at those locations does not become homo. The rate of crossing is
different for each area, and because it is defined more or less precisely, the rate at
which hetero gene positions become homo as a result of gynogenesis varies greatly
by position. Depending on the genetic trait, it can therefore be difficult to obtain
homo genes for that trait through gynogenesis.
4.3 Cell Manipulation
Cells are structural and functional units for nearly every organism on the planet.
A biological organism is, in a sense, a society of cells. Cells typically measure 10–
30 lm and are surrounded by a membrane, with one nucleus and cytoplasm inside
(Fig. 4.4). Cell biology, which seeks to use the cell as a basis for explicating
biological phenomena, was established as a field in the early 19th century. Subsequent advancements led to the development of various sophisticated techniques
for manipulating these tiny cells. Some of these techniques may be applied as is to
the field of biotechnological breeding.
The chromosome manipulation described in the preceding section may be
characterized as cell manipulation as well, in that it involves gamete cells. The
academic context is slightly different, however, and actual techniques applied with
larger fish consist mainly of manipulation of individual organisms by holding them
by the armpit or grabbing them barehanded to squeeze out roe or sperm; roe, which
measure 1 mm or more in diameter, are handled in the dozens to thousands, while
sperm is handled in units of several cubic centimetre. Since the cell manipulation
described below does not typically require sophisticated techniques, it has been
divided into several categories (Oshiro 1990).
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4 Fish Breeding and Biotechnology
organisms are nearly identical genetically. Homozygotic clones are referred to as a
“pure line.” Several repetitions of gynogenesis were expected to result in establishment of a pure line in the generation faster than with inbreeding. If no crossing
occurs at all between homologous chromosomes at a synapsis during maturation
division, blocking of second polar body emission to form a gynogenetic diploid
results in the position of heterosynaptic genes becoming homosynaptic, producing
an organism that is homosynaptic for all genetic positions (homosynaptic
organism).
For the second gynogenetic generation from these female parents, homosynaptic
groups (clones) appear that always have the same genes at the same gene locations.
Indeed, crossing occurs between homologous chromosomes, and the position of
hetero genes at those locations does not become homo. The rate of crossing is
different for each area, and because it is defined more or less precisely, the rate at
which hetero gene positions become homo as a result of gynogenesis varies greatly
by position. Depending on the genetic trait, it can therefore be difficult to obtain
homo genes for that trait through gynogenesis.
4.3 Cell Manipulation
Cells are structural and functional units for nearly every organism on the planet.
A biological organism is, in a sense, a society of cells. Cells typically measure 10–
30 lm and are surrounded by a membrane, with one nucleus and cytoplasm inside
(Fig. 4.4). Cell biology, which seeks to use the cell as a basis for explicating
biological phenomena, was established as a field in the early 19th century. Subsequent advancements led to the development of various sophisticated techniques
for manipulating these tiny cells. Some of these techniques may be applied as is to
the field of biotechnological breeding.
The chromosome manipulation described in the preceding section may be
characterized as cell manipulation as well, in that it involves gamete cells. The
academic context is slightly different, however, and actual techniques applied with
larger fish consist mainly of manipulation of individual organisms by holding them
by the armpit or grabbing them barehanded to squeeze out roe or sperm; roe, which
measure 1 mm or more in diameter, are handled in the dozens to thousands, while
sperm is handled in units of several cubic centimetre. Since the cell manipulation
described below does not typically require sophisticated techniques, it has been
divided into several categories (Oshiro 1990).
88
4 Fish Breeding and Biotechnology