This document discusses quantitative trait locus (QTL) mapping and the inclusive composite interval mapping (ICIM) method. It begins with an overview of quantitative traits, QTL mapping, and different mapping populations. It then describes problems with previous interval mapping methods and introduces the theoretical basis and methodology of ICIM, which can detect additive and interacting QTL while avoiding biased estimates. The document highlights several publications that have used ICIM in crops like rice, wheat, soybean, and maize. It concludes with an overview of the biparental population (BIP) functionality in the QTL IciMapping software, which implements six different QTL mapping methods including various interval mapping approaches and single marker analysis.
QTL is a gene or the chromosomal region that affects a quantitative trait, which should be polymorphic (have allelic variation) to have an effect in a population, must be linked to a polymorphic marker allele to be detected. The QTL mapping consists of 4 steps, like the development of mapping population, generation of polymorphic marker data set among the parents, construction of linkage map, and finally the QTL analysis
All the above steps are described in these slides very briefly along with two case studies.
Microsatellite are powerful DNA markers for quantifying genetic variations within & between populations of a species, also called as STR, SSR, VNTR. Tandemly repeated DNA sequences with the repeat/size of 1 – 6 bases repeated several times
Quantitative trait loci (QTL) analysis and its applications in plant breedingPGS
Abstract
Many agriculturally important traits such as grain yield, protein content and relative disease resistance are controlled by many genes and are known as quantitative traits (also polygenic or complex traits). A quantitative trait depends on the cumulative actions of many genes and the environment. The genomic regions that contain genes associated with a quantitative trait are known as quantitative trait loci (QTLs). Thus, a QTL could be defined as a genomic region responsible for a part of the observed phenotypic variation for a quantitative trait. A QTL can be a single gene or a cluster of linked genes that affect the trait. The effects of individual QTLs may differ from each other and change from environment to environment. The genetics of a quantitative trait can often be deduced from the statistical analysis of several segregating populations. Recently, by using molecular markers, it is feasible to analyze quantitative traits and identify individual QTLs or genes controlling the traits of interest in breeding programs.
QTL is a gene or the chromosomal region that affects a quantitative trait, which should be polymorphic (have allelic variation) to have an effect in a population, must be linked to a polymorphic marker allele to be detected. The QTL mapping consists of 4 steps, like the development of mapping population, generation of polymorphic marker data set among the parents, construction of linkage map, and finally the QTL analysis
All the above steps are described in these slides very briefly along with two case studies.
Microsatellite are powerful DNA markers for quantifying genetic variations within & between populations of a species, also called as STR, SSR, VNTR. Tandemly repeated DNA sequences with the repeat/size of 1 – 6 bases repeated several times
Quantitative trait loci (QTL) analysis and its applications in plant breedingPGS
Abstract
Many agriculturally important traits such as grain yield, protein content and relative disease resistance are controlled by many genes and are known as quantitative traits (also polygenic or complex traits). A quantitative trait depends on the cumulative actions of many genes and the environment. The genomic regions that contain genes associated with a quantitative trait are known as quantitative trait loci (QTLs). Thus, a QTL could be defined as a genomic region responsible for a part of the observed phenotypic variation for a quantitative trait. A QTL can be a single gene or a cluster of linked genes that affect the trait. The effects of individual QTLs may differ from each other and change from environment to environment. The genetics of a quantitative trait can often be deduced from the statistical analysis of several segregating populations. Recently, by using molecular markers, it is feasible to analyze quantitative traits and identify individual QTLs or genes controlling the traits of interest in breeding programs.
Association genetics‟ or ‟association studies,” or ‟linkage disequilibrium mapping”.
Tool to resolve complex trait variation down to the sequence level by exploiting historical and evolutionary recombination events at the population level.
Natural population surveyed to determine MTA using LD.
Association mapping, also known as "linkage disequilibrium mapping", is a method of mapping quantitative trait loci (QTLs) that takes advantage of linkage disequilibrium to link phenotypes to genotypes.Varioius strategey involved in association mapping is discussed in this presentation
Multiple inbred founder lines are inter-mated for several generations prior to creating inbred lines, resulting in a diverse population whose genomes are fine scale mosaics of contributions from all founders.
Strategies for mapping of genes for agronomic traits in plantstusharamodugu
The genomic regions associated with the expression of a quantitative trait is referred to as quantitative trait loci (QTL).
A QTL may contain one or more genes affecting the concerned quantitative trait.
Sax(1923) reported linkage between seed coat colour and seed size, which are qualitative and quantitative traits in common bean and the work highlighted the basic principles for mapping of polygenes based on the detection of association between a quantitative trait phenotype and a genetic marker.
Thoday (1961) explored this QTL concept further by combining elaborate cytogenetic techniques with genetic analysis to map QTLs for several quantitative traits in Drosophila
Introduction:
Proposed by Meuwissen et al. (2001)
GS is a specialized form of MAS, in which information from genotype data on marker alleles covering the entire genome forms the basis of selection.
The effects associated with all the marker loci, irrespective of whether the effects are significant or not, covering the entire genome are estimated.
The marker effect estimates are used to calculate the genomic estimated breeding values (GEBVs) of different individuals/lines, which form the basis of selection.
Why to go for genomic selection:
Marker-assisted selection (MAS) is well-suited for handling oligogenes and quantitative trait loci (QTLs) with large effects but not for minor QTLs.
MARS attempts to take into account small effect QTLs by combining trait phenotype data with marker genotype data into a combined selection index.
Based on markers showing significant association with the trait(s) and for this reason has been criticized as inefficient
The genomic selection (GS) scheme was to rectify the deficiency of MAS and MARS schemes. The GS scheme utilizes information from genome-wide marker data whether or not their associations with the concerned trait(s) are significant.
GEBV: GenomicEstimated Breeding Values-
The sum total of effects associated with all the marker alleles present in the individual and included in the GS model applied to the population under selection
Calculated on a single individual basis
Gene-assisted genomic selection:
A GS model that uses information about prior known QTLs, the targeted QTLs were accumulated in much higher frequencies than when the standard ridge regression was used
The sum total of effects associated with all the marker alleles present in the individual and included in the GS model applied to the population under selection
Calculated on a single individual basis
Population used:
Training population: used for training of the GS model and for obtaining estimates of the marker-associated effects needed for estimation of GEBVs of individuals/lines in the breeding population.
Breeding population: the population subjected to GS for achieving the desired improvement and isolation of superior lines for use as new varieties/parents of new improved hybrids.
Training population-
large enough: must be representative of the breeding population: max. trait variance with marker : by cluster analysis
should have either equal or comparable LD, LD decay rates with breeding populations
Updated by including individuals/lines from the breeding population
Training more than one generation
Low colinearity between markers is needed since high colinearity tends to reduce prediction accuracy of certain GS models. (colinearity disturbed by recombination)
QTL mapping is the statistical study of the allels that occur in a locus and phenotypes that they produce.
Common name : Maize/ corn
Scientific name : Zea mays
No of chromosomes : 20
Linkage groups : 10
A total of 220 molecular markers were used in construction of linkage maps and to map QTL. One-hundred and six (RFLP) probes were
mapped to 110 diVerent loci for additional information
regarding the RFLPs In addition to the RFLPs, 32 SSRs and 78 SNPs were used to
construct the linkage map.
Used Mapping Population is : Back cross population
No of populations used : 02
Population size : 337 (144 & 193)
Disease chosen for QTLs : southern leaf blight (SLB)
QTL Cartographer version 2.5 was used for dQTL mapping.
Association genetics‟ or ‟association studies,” or ‟linkage disequilibrium mapping”.
Tool to resolve complex trait variation down to the sequence level by exploiting historical and evolutionary recombination events at the population level.
Natural population surveyed to determine MTA using LD.
Association mapping, also known as "linkage disequilibrium mapping", is a method of mapping quantitative trait loci (QTLs) that takes advantage of linkage disequilibrium to link phenotypes to genotypes.Varioius strategey involved in association mapping is discussed in this presentation
Multiple inbred founder lines are inter-mated for several generations prior to creating inbred lines, resulting in a diverse population whose genomes are fine scale mosaics of contributions from all founders.
Strategies for mapping of genes for agronomic traits in plantstusharamodugu
The genomic regions associated with the expression of a quantitative trait is referred to as quantitative trait loci (QTL).
A QTL may contain one or more genes affecting the concerned quantitative trait.
Sax(1923) reported linkage between seed coat colour and seed size, which are qualitative and quantitative traits in common bean and the work highlighted the basic principles for mapping of polygenes based on the detection of association between a quantitative trait phenotype and a genetic marker.
Thoday (1961) explored this QTL concept further by combining elaborate cytogenetic techniques with genetic analysis to map QTLs for several quantitative traits in Drosophila
Introduction:
Proposed by Meuwissen et al. (2001)
GS is a specialized form of MAS, in which information from genotype data on marker alleles covering the entire genome forms the basis of selection.
The effects associated with all the marker loci, irrespective of whether the effects are significant or not, covering the entire genome are estimated.
The marker effect estimates are used to calculate the genomic estimated breeding values (GEBVs) of different individuals/lines, which form the basis of selection.
Why to go for genomic selection:
Marker-assisted selection (MAS) is well-suited for handling oligogenes and quantitative trait loci (QTLs) with large effects but not for minor QTLs.
MARS attempts to take into account small effect QTLs by combining trait phenotype data with marker genotype data into a combined selection index.
Based on markers showing significant association with the trait(s) and for this reason has been criticized as inefficient
The genomic selection (GS) scheme was to rectify the deficiency of MAS and MARS schemes. The GS scheme utilizes information from genome-wide marker data whether or not their associations with the concerned trait(s) are significant.
GEBV: GenomicEstimated Breeding Values-
The sum total of effects associated with all the marker alleles present in the individual and included in the GS model applied to the population under selection
Calculated on a single individual basis
Gene-assisted genomic selection:
A GS model that uses information about prior known QTLs, the targeted QTLs were accumulated in much higher frequencies than when the standard ridge regression was used
The sum total of effects associated with all the marker alleles present in the individual and included in the GS model applied to the population under selection
Calculated on a single individual basis
Population used:
Training population: used for training of the GS model and for obtaining estimates of the marker-associated effects needed for estimation of GEBVs of individuals/lines in the breeding population.
Breeding population: the population subjected to GS for achieving the desired improvement and isolation of superior lines for use as new varieties/parents of new improved hybrids.
Training population-
large enough: must be representative of the breeding population: max. trait variance with marker : by cluster analysis
should have either equal or comparable LD, LD decay rates with breeding populations
Updated by including individuals/lines from the breeding population
Training more than one generation
Low colinearity between markers is needed since high colinearity tends to reduce prediction accuracy of certain GS models. (colinearity disturbed by recombination)
QTL mapping is the statistical study of the allels that occur in a locus and phenotypes that they produce.
Common name : Maize/ corn
Scientific name : Zea mays
No of chromosomes : 20
Linkage groups : 10
A total of 220 molecular markers were used in construction of linkage maps and to map QTL. One-hundred and six (RFLP) probes were
mapped to 110 diVerent loci for additional information
regarding the RFLPs In addition to the RFLPs, 32 SSRs and 78 SNPs were used to
construct the linkage map.
Used Mapping Population is : Back cross population
No of populations used : 02
Population size : 337 (144 & 193)
Disease chosen for QTLs : southern leaf blight (SLB)
QTL Cartographer version 2.5 was used for dQTL mapping.
This presentation provides an introduction to quantitative trait loci (QTL) analysis and marker-assisted selection (MAS) in plant breeding. The presentation begins by explaining the type of quantitative traits. The process of QTL analysis, including the use of molecular genetic markers and statistical methods, is discussed. Practical examples demonstrating the power of MAS are provided, such as its use in improving crop traits in plant breeding programs. Overall, this presentation offers a comprehensive overview of these important genomics-based approaches that are transforming modern agriculture.
Quantitative Image Analysis for Cancer Diagnosis and Radiation TherapyWookjin Choi
1.Lung Cancer Screening
1.1.Deep learning (feasible but not interpretable)
1.2.Radiomics (concise model)
1.3.Spiculation quantification (interpretable feature)
2.PET/CT Tumor Response
2.1.Aggressive Lung ADC subtype prediction (helpful for surgeons)
2.2.Pathologic response prediction (accurate but not concise)
2.3.Local tumor morphological changes (accurate and interpretable)
Towards fine mapping of drought tolerance related QTL region in chickpea (Cic...ICRISAT
Terminal drought is one of major constraints that lead to considerable yield losses (~50%) in chickpea. By using linkage mapping approach on ICC 4958 × ICC 1882 population, a genomic region (~35cM) harbouring several QTLs for drought tolerance related traits was identified on linkage group 4 (LG04).
16 May 2014
large data set is not available for some disease such as Brain Tumor. This and part2 presentation shows how to find "Actionable solution from a difficult cancer dataset
“MS-Extractor: An Innovative Approach to Extract Microsatellites on „Y‟ Chrom...IJERD Editor
Simple Sequence Repeats (SSR), also known as Microsatellites, have been extensively used as
molecular markers due to their abundance and high degree of polymorphism. The nucleotide sequences of
polymorphic forms of the same gene should be 99.9% identical. So, Microsatellites extraction from the Gene is
crucial. However, Microsatellites repeat count is compared, if they differ largely, he has some disorder. The Y
chromosome likely contains 50 to 60 genes that provide instructions for making proteins. Because only males
have the Y chromosome, the genes on this chromosome tend to be involved in male sex determination and
development. Several Microsatellite Extractors exist and they fail to extract microsatellites on large data sets of
giga bytes and tera bytes in size. The proposed tool “MS-Extractor: An Innovative Approach to extract
Microsatellites on „Y‟ Chromosome” can extract both Perfect as well as Imperfect Microsatellites from large
data sets of human genome „Y‟. The proposed system uses string matching with sliding window approach to
locate Microsatellites and extracts them.
Data Con LA 2022 - Early cancer detection using higher-order genome architectureData Con LA
My (Angela) Chung, Data Enthusiast, San Jose State University
Cancer is a complex disease which requires interactions between cell-intrinsic alterations and tumor microenvironment. The connection between epigenetics and genomic structure plays a key role in chromatin interactions and enhancer-promoter communications for transcriptional activities. Alterations of these components in oncogenic signaling pathway potentially cause cancer cell-intrinsic changes and inappropriate instructions to normal cell cycles, leading to abnormal cell growth.
' Topologically associating domains (TADs) and A/B compartments are the main structures of higher-order chromatin structure. These contact domains, chromatin states, super-enhancers, and histone modifications together regulate transcription and gene expression for normal/abnormal cell cycles.
' Several bioinformatics tools were utilized ' FANC for processing raw FASTQ data to Hi-C contact matrices, JuicerTools for obtaining the locations of contact domains on the entire genome, and CoolBox for visualizing chromatin contacts in different cell lines.
' High-resolution chromatin contacts showed dynamic interactions among chromosomal regions in different cell lines.
' Qualitative and quantitative features were comprehensively engineered from 3D chromatin folding and epigenetic regulators using available packages (scikit learn, pytorch, pandas, numpy, matplotlib, etc.).
' XGBoost multi-class classifier achieved the highest accuracy of 80.90% in classifying normal and cancer cell lines based on chromatin interactions, followed by Random Forest at 73.76% and TabNet classifier at 70.00%.
In this presentation, we will delve into the principles of QTL mapping and explore various strategies for mapping QTLs in plants. We will also discuss the advantages and limitations, and provide insights into how QTL mapping is advancing our understanding of genetics.
Similar to Jiankang Wang. Principle of QTL mapping and inclusive composite interval mapping (ICIM) (20)
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
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Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
In silico drugs analogue design: novobiocin analogues.pptx
Jiankang Wang. Principle of QTL mapping and inclusive composite interval mapping (ICIM)
1. 1
Principle of QTL mapping and
Inclusive Composite Interval
Mapping (ICIM)
Jiankang Wang
CIMMYT China and CAAS
E-mail: wangjk@caas.net.cn or jkwang@cgiar.org
The 9th Workshop on QTL Mapping and Breeding Simulation
The University of Sydney, Cobbitty NSW, 7-9 March 2012
2. Outlines
Quantitative traits and QTL mapping
Inclusive composite interval
mapping (ICIM) for additive and
interacting QTL
Selected publications using ICIM
The BIP functionality in QTL
IciMapping
2
4. Quantitative traits
Continuous phenotypic variation
Affected by many genes
Affected by environment
Epistasis
Polygene (or multi-factorial )
hypothesis
Classical quantitative genetics
4
5. What is QTL Mapping?
The procedure to map individual genetic factors
with small effects on the quantitative traits, to
specific chromosomal segments in the genome
The key questions in QTL mapping studies are:
How many QTL are there?
Where are they in the marker map?
How large an influence does each of them
have on the trait of interest?
5
6. 6
Dataset of QTL mapping
Mapping population
Marker data of each individual in
the mapping population
Linkage map
Phenotypic data
8. 8
Classification of mapping
populations
Bi-parental mapping populations (linkage
mapping)
Temporary population: F2 and BC
Permanent population: RIL, DH, CSSL
Secondary population
Association mapping
Natural populations: human and animals
9. 9
Overview on
QTL mapping methods
Single marker analysis (Sax 1923; Soller et al. 1976)
The single marker analysis identifies QTLs based on the difference
between the mean phenotypes for different marker groups, but cannot
separate the estimates of recombination fraction and QTL effect.
Interval mapping (IM) (Lander and Botstein 1989)
IM is based on maximum likelihood parameter estimation and provides
a likelihood ratio test for QTL position and effect. The major
disadvantage of IM is that the estimates of locations and effects of QTLs
may be biased when QTLs are linked.
Regression interval mapping (RIM)
(Haley and Knott 1992; Martinez and Curnow 1992 )
RIM was proposed to approximate maximum likelihood interval mapping
to save computation time at one or multiple genomic positions.
10. 10
Composite interval mapping (CIM) (Zeng 1994)
CIM combines IM with multiple marker regression analysis,
which controls the effects of QTLs on other intervals or
chromosomes onto the QTL that is being tested, and thus
increases the precision of QTL detection.
Multiple interval mapping (MIM) (Kao et al. 1999)
MIM is a state-of-the-art gene mapping procedure. But
implementation of the multiple-QTL model is difficult, since the
number of QTL defines the dimension of the model which is
also an unknown parameter of interest.
Bayesian model (Sillanpää and Corander 2002)
In any Bayesian model, a prior distribution has to be
considered. Based on the prior, Bayesian statistics derives the
posterior, and then conduct inference based on the posterior
distribution. However, Bayesian models have not been widely
used in practice, partially due to the complexity of
computation and the lack of user-friendly software.
11. 11
Principle of QTL mapping
Three marker types at one marker locus
A. 很可能存
在QTL和标
记的连锁
性状平均数
mm MMMm
B. 不一定存
在QTL和标
记的连锁
性状平均数
mm MMMm
12. 12
Backcrosses (P1BC1 and P2BC1)
of P1: MMQQ and P2: mmqq
BC1 BC2
Genotype Frequency
Genotypic
value
Genotype Frequency
Genotypic
value
MMQQ )1(2
1
r− m+a MmQq )1(2
1
r− m+d
MMQq r2
1
m+d Mmqq r2
1
m-a
MmQQ r2
1
m+a mmQq r2
1
m+d
MmQq )1(2
1
r− m+d mmqq )1(2
1
r− m-a
13. 13
Principle of single marker
analysis (P1BC1 as example)
Two marker types:
Difference in phenotype between the two types
MMQqMMQQMM )1( µµµ rr +−=
rdarmdmramr +−+=+++−= )1()())(1(
MmQqMmQQMm )1( µµµ rr −+=
drramdmramr )1())(1()( −++=+−++=
))(21(MmMM dar −−=− µµ
14. 14
Interval mapping (IM)
(Lander and Botstein 1989)
Linear model (j=1,2,…,n )
b* represent QTL effect, is the indicator
variable (0 or 1) for QTL genotype
Likelihood profile
Support interval: One-LOD interval
*
jx
jji exbby ++= **
0
15. 15
QTL genotypes under each marker
type in P1BC1 (double crossover not considered)
P1: P2:
F1: P1:
区间标记类型1 区间标记类型2 区间标记类型3 区间标记类型4
Mi Q Mi +1
Mi Q Mi +1
mi q mi +1
mi q mi +1
×
Mi Q Mi +1 Mi Q Mi +1
Mi Q Mi +1
×
Mi Q Mi +1 Mi Q Mi +1 Mi Q Mi +1 Mi Q Mi +1
Mi Q Mi +1 Mi Q mi +1 mi q mi q mi +1
Mi Q Mi +1
Mi q mi +1
mi q Mi +1
Mi Q Mi +1
mi Q Mi +1
mi q mi +1
Marker class I Marker class II Marker class III Marker class IV
17. 17
Problems with IM
Assumption: No more than one QTL
per chromosome or linkage group
“Ghost QTL” for linked QTL
Large confidence interval
Biased effect estimation
Composite interval mapping (CIM)
(Zeng 1994)
18. 18
Problems with CIM
In the algorithm of CIM, both QTL effect at the
current testing position and regression coefficients
of the marker variables used to control genetic
background were estimated simultaneously in an
expectation and maximization (EM) algorithm.
Thus, this algorithm could not completely ensure
that the effect of QTL at current testing interval
was not absorbed by the background marker
variables and therefore may result in biased
estimation of the QTL effect.
25. In rice
Crop Science (2008) 48: 1799-1806; Tiller
angle
Hereditas (2009) 146: 67-73; Brown
planthopper resistance
Mol. Breeding (2010) 25: 287-298; Heading
date
Scientia Agricultura Sinica 2010,43(21):
4331-4340; Nitrogen efficiency
25
26. In wheat
Euphytica (2009) 165: 435-444; flour and noodle
color components and yellow pigment content
26
27. More in wheat
Acta Agronomica Sinica (2011) 37 (2): 294-301; Coleoptile
Length and Radicle Length
Crop & Pasture Science (2009) 60: 587-597; White salted
noodle quality
Crop & Pasture Science (2011) 62: 625-638; Kernel morphology
traits
Mol. Breeding (2010) 25: 615-622; Adult-plant resistance to
powdery mildew
Theor. Appl. Genet. (2009) 119: 1349-1359; Adult-plant
resistance to stripe rust
Mol. Breeding (2011) on line published; Grain protein content
and grain yield component
Scientia Agricultura Sinica 2011,44(14):2857-2867; Grain yield
per plant and plant height
27
28. In soybean
Breeding Science
(2008) 58: 355-359 ;
Salt tolerance
ACTA
AGRONOMICA SINICA
2009, 35(12):
2139−2149; Protein
Related Traits
28
29. In Maize
Theor. Appl. Genet. (2011) 123: 327-338;
Partial restoration of male fertility of C-type
cytoplasmic male sterility
Plant Mol. Biol. Rep. (2011) on line published;
Nitrogen Use Efficiency
HEREDITAS 32(6): 625-631; The area of
leaves
29