Agriculture Reference
In-Depth Information
Genome 2
Genome 1
X
Cross-breeding
Gene of interest
Transgene technology
Gene transfer
Gene isolation
Fig. 2.1.
Comparison of cross-breeding with transgene technology (or genetic modifi cation technology)
to introduce a gene of interest (encoding a trait of interest) present in genome 1 into a well-performing
variety of genome 2. By breeding, crossing is needed between one parent of the well-performing variety
and the other parent containing the trait of interest. Thereby, both genomes are mixed and many
backcrosses are needed to obtain again the well-performing variety while keeping the trait of interest. By
genetic modifi cation, a trait from any organism can be isolated and introduced into the well-performing
background without dragging along unwanted genetic information.
individuals is then needed to identify the
mutant plants with the desired traits.
Moreover, this is only possible for traits that
are easy to measure at the phenotypic level.
techniques allow whole cells or parts of cells
to fuse to create composites or chimeras
from unrelated species. h e main problem
has been the instability of the new genome
combinations from two dissimilar species.
h erefore, the use of somatic hybridization
in breeding programmes has, in practice,
been restricted to the introgression of genes
from related plant species.
Chromosome doubling, by making use of
colchicine, has been used intensively in the
breeding of fodder crops, as often the
derived polyploid varieties resulted in higher
yield. Polyploidization is also a key tech-
nology for the creation of fertile interspecii c
hybrids, as it allows crosses between related
plants with dif erent ploidy levels. In this
way, wild relatives could, after genome
doubling, be crossed with crop species. h is
has been used, for example, for the intro-
duction of pathogen-resistance genes from
wild potato relatives into varieties of the
cultivated potato.
modifi cation
Since the 1990s, the focus of breeding has
shifted towards transgenesis and variants
such as cisgenesis. Genetic modii cation
(GM) is dif erent from the previously
described tools and traditional breeding in
that any modii cation can be designed and
tailored to achieve the desired ef ect (see Fig.
2.1). h is GM methodology is more precise,
has very limited problems with genome
instability and the success rate is much
higher than with mutagenesis, interspecii c
crosses and somatic hybridization. It is not
only restricted to the introduction of new
genes but can also be used to modify the
expression of endogenous genes, or it can
shut down the expression of genes coding
for undesired traits. Already in an early
Somatic hybridization is a technique used to
introduce novel genes into a crop genome
from a donor species with which the
crop will normally not interbreed. More
sophisticated microinjection and cell fusion
