Download basic features of breeding

BREEDING BASED ON
THE GENETIC
RECOMBINATION
PRINCIPLE
Taryono
Faculty of Agriculture
Gadjah Mada University
Hybridization
 It is a combining in the future strains the useful traits and
characters inherent in each parent separately
 it has become the predominant method of improvement of
cultivated strains due to hybrid vigor
 It is known as combination breeding
 Distinction is made between intra- and interspecific crossing
 The successful of hybridization is to great extent dependent on the
selection of parental materials and how well the breeder is
familiar with the genetic processes occurring in the segregating
progenies of hybrid populations
 The choice of parents might seem the best starting point, but in
practice, it is better to expound crossing and selection schemes
first and then to consider the source and choice of parents in the
wider context of breeding strategy
Hybridization
 The material resulting from hybridization is used in
different ways
1. for selection in the breeding of selection strains (open pollinated
strains)
2. directly in the production as first generation hybrids (hybrid
strains)
 The improvement of cross pollinated organisms cannot
be based on isolation of homozygous genotypes
1. As a consequence of outbreeding, any strain of outbreeding
organism has heterogenous genotypes, each being to some extent
different from the other ones in a given population
2. Induced selfing of outbreeding organisms leads to inbreeding
depression of the offspring
Hybridization
 Sexual recombination in fish might occasionally happen
in nature, but most were conducted artificially
 The principle of artificial sexual recombination is to
impose the male and female gametes of different
fishes to fuse together as a zygote by artificial methods
that does not happen in natural conditions
 Those hybrid zygotes will develop into hybrids with
some improved characteristics
 The modified phenotypes appeared in those hybrids is
the result of “hybridity expression” of the newly
reconstructed genomes of the individuals
 Sexual recombination is very useful for producing
better F1 hybrids
Hybridization



Sexual recombination only generally can be done
between taxonomically closely related species
In fish, sexual recombination not only can be
successfully made among closely related species, but
also can be applied to those fish species which belong
to rather distantly related species
Inter-genus sexual hybridization
Cyprinus carpio x Carassius auratus

Inter-subfamily sexual hybridization
Ctenophry idellus (sub-fam. Leucinae) x Megalobrama
amblycephala (Sub-fam. Abramidinae)

Inter-order combination
Carassius auratus (order Cypriniformes) x Oreochromis nilotica
(order Perciformis)
Natural barrier in distance
recombination
1.
2.
3.
4.
The failure of foreign sperm to penetrate the egg
Foreign sperm can enter the eggs but it will be degenerated and
disappear in the egg cytoplasm without performing any vital
function
Foreign sperm can enter the egg and enlarge as a male
pronucleus but it can not fuse with the egg to form a zygote
nucleus
Foreign sperm can enter the egg and enlarge as a male
pronucleus but it can fuse with the egg to form a zygote nucleus
and divide in coordinating with egg cytoplasmic division,
however due to unknown natural incompatibility which existed
between the sperm and egg, the hybrid zygote nucleus will
become heteroploid. The embryo develops abnormally
Open pollinated populations (OPP)
 The improvement of OPP depends essentially upon the
changing gene frequencies towards fixation of
favorable allele while maintaining a high degree of
heterozygosity
 Uniformity is impossible and trueness to type is a
statistically feature of the population as a whole, not a
characteristic of individual plant
 Two types
1. Population improvement
a population is changed by the chosen selection procedures based
on purely phenotypic selection (mass selection)
2. Synthetic
population improvement which has to be reconstructed from
parental lines. t can be constructed from combining inbred, clones
as a parent
Heterosis
1. It implies increased vigor of the first
generation hybrids as compared to the
parental forms
2. It manifests itself fully in the first generation,
whereas in the subsequent generation the
hybrid vigour goes down substantially
3. Heterotic hybrid seed can be sown
commercially once
4. Practical utilization of heterosis involves
annual crossing to produce heterotic hybrid
seed
Nuclear transplantation
 It is a diploid nucleus into enucleated egg.
 It is to combine the nucleus and cytoplasm of different
species to produce nucleo-cytoplasmic hybrids
1. Inter-genus combination
Nucleus of common carp and cytoplasm from crusian carp. Adult
fish with essentials of common carp phenotype and cytoplasmic
influenced character at morphological, physiological and
biochemical levels were obtained. Both male and female hybrids
are fertile
2. Inter –subfamily combination
Nucleus from grass carp and cytoplasm of blunt snout bream. Adult
fishes were obtained.