CAPÍTULO 2: MARCO TEÓRICO
2.5. PROGRAMAS DE DEPORTE ESCOLAR
2.5.3. Revisión bibliográfica sobre el PIDEMSG
genetic markers linked to QTL in tree breeding schemes. QTL mapping experiments need to be optimised to minimise costs of data collection and genotyping. In Chapter
2,
the expressions for variance components for single-marker ANOV A were derived to help determine the size of experimental designs for detecting QTL in full-sib families where parents are assumed to heterozygous for different marker alleles. The effects of experimental and genetical parameters on the power of linkage detection were evaluated. For a given experimental size, fewer larger families were better than many small families. Recombination rate, size and dominance properties of the QTL were found to have large effects on the power of linkage detection.
Molecular markers are being increasingly used in self-families of outbred organisms to find genes causing inbreeding depression in growth traits. Some of the QTL in self families will represent genetic load; however, there would be some individuals without appreciable load so QTL detected in these self-families would be similar to those expressed under the normal course of outbreeding. In Chapter
3,
the methodology for estimating the power of QTL detection in self-families of outbred populations is presented. The power of linkage detection was calculated for a wide range of progeny sizes and genetic parameters at the QTL. The magnitude of the gene effect and the recombination rate were found to have enormous effect of the power of linkage detection.An experiment involving a full-sib pedigree
(850.055
x850.096)
was established atForest Research
to determine the genetic location and effects of genomic regions controlling wood density at three stages (rings corresponding to ages1-5, 6- 10
and outer wood density). In Chapter3,
analysis of only a single linkage group(three)
of the parent850.055
was considered for mapping QTL. A multiple marker least-square approach was employed for mapping QTL for each of the three traits. Experimentwise critical values, which accounted for the evaluation of marker-QTL associations across the whole genome and for three correlated traits, were calculated. Logistic regression was used for multiple-trait QTL mapping. A putative QTL with large effect on juvenile wood density (rings corresponding to ages1-5)
appears to be segregating at73
cM position (experimentwiseP<O.Ol ).
The width of the95
% bootstrap confidence interval for the putative QTL was40
cM (i.e.56-96
cM).Summary
1 13
In Chapter
5,
stochastic simulation was undertaken to investigate the genetic response from within-family MAS. Genetic.gains obtained using MAS were compared with those obtained from conventional strategies for three selection and deployment options: 'full-sib family forestry' , 'clonal forestry' and 'forwards selection for deployment' . The genetic model contained polygenes and a QTL linked to a marker. Heritability of the trait was assumed to be either0.25
or0.75.
A QTL that explained20
% of the genetic variance was used. It was assumed that linkage phase and the haplotype in the base population was known in order to simulate transmission of haplotype. Relative genetic gain due to the use of marker was6-8
% and2-3
% for 'full-sib family forestry' and 'clonal forestry' options, respectively.Index selection is a tool commonly employed in tree breeding programs. In Chapter
6,
a method is proposed to reduce the effect of sampling errors on the estimates of multivariate genetic parameters, thus increasing the efficiency of index selection. The proposed method consists of 'regressing' the estimated (least-squares) selection index coefficients towards the relative economic values. Using Monte Carlo simulations, the efficiency of the proposed method was found to be very high when the number of families used in the progeny tests are few. When the heritability of index traits was low and their relative economic values were in opposite order to heritability, the efficiency of the proposed method was much higher. The application of the proposed method was explored only for the traditional index selection and its efficiency for multitrait MAS remains to be evaluated.In the general discussion, different QTL analysis methods i.e., single-marker ANOV A, interval mapping and mUltiple marker methods are outlined and discussed. Calculating the threshold levels in QTL mapping studies is always crucial. Different approaches to calculate critical values are outliIled. Various aspects of designs of QTL mapping experiments in forest trees are discussed. Different strategies for increasing the power of marker-QTL linkage detection are outlined and discussed. It was shown that most of the power of linkage detection could be achieved by selectively genotyping
5-10
% of the total offspring from each tail of the trait distribution. Implementation of MAS in radiata pine breeding program in New Zealand is also discussed. Different selection and deployment scenarios are outlined where MAS can be applied in the near future.1 14
Curriculum vitae
Satish Kumar was born on May
21st 1965
in Bakheta, Rohtak, India. He completed secondary school education in198 1
from S . M. Hindu High School, Sonepat, India. He completed his tertiary education, B . Sc. (Honours) Agriculture, in1 986
from Haryana Agricultural University, Hisar, India. During1986
to1988,
he studied at G. B . Pant University of Agriculture and Technology, Pantnagar, India, and obtained M. Sc. (Agricultural Statistics) while receiving a Graduate Research Assistantship. From1989
to