Geoscience Reference
In-Depth Information
Specific
significant
considerations
throughout
scheming of a
BC/MAS
structure
Transfer of specific favourable alleles at a target locus from a
donor line to a recipient line with marker assistance is the basic
strategy of BC/MAS system. The employment of DNA markers
will increase the rapidity of the selection process by separation
of progeny at the genotypic level in every generation. In a wide
range, the BC scheme targets either at complete or partial line
conversion. Complete line conversion involves development of a
line that has precisely the same genetic composition as the recipi-
ent line, excluding target loci where the presence of homozygous
alleles from a donor line is anticipated. The objective of partial
line conversion is to develop a line that will have a small pro-
portion of the scattered donor genome over its genome (recipi-
ent parent) along with desirable homozygous alleles of the target
gene. Numerous factors influence the efficiency and effective-
ness of a BC/MAS scheme like the number of target genes, the
distance between the flanking markers and also the target gene
(2-20 cM), and similarly the variety of genotypes designated in
every BC generation. Relying upon the objectives, the experi-
mental design for line conversion through BC/MAS desires has
to be designed based on the obtainable resources, the nature of
the germplasm (e.g. agronomical quality and variety of lines to
be improved) and technical options available at the marker level.
As soon as the number of target genes to be transferred are out-
lined, a future step would be to work out the population size that
must be screened at every generation, giving a target-selectable
population size of 50-100 genotypes. Henceforth, one ought to
confirm the fascinating recombination frequency between the
flanking markers and the target. Also the number of genotypes
designated at each generation supported the target and also the
constraints of the experiment. The number of BC generations
required to accomplish the introgression can be foreseen based on
simulations. Whereas resources are limited or introgression from
a donor line into an outsized range of recipient lines is desired,
strategies based on BC/MAS at one target locus exclusively at
one advanced BC generation should be considered. Selection in
later generations is additionally helpful because the ratio of the
standard deviation of the mean of the donor genome contribution
increases as the backcrossing proceeds. The backcross procedure
can be finished after four, rather than six, backcross generations,
even with small population sizes and limited number of marker
data points (MDP). Therefore, the marker technology is useful
even when the resources in a very breeding programme are lim-
ited. MAS has the potential to recover a maximum proportion
of recurrent parent genomes up to BC3 generation, which is not
attainable via a typical backcross breeding process (the same
