dlmap: Perform DLMapping

Description Usage Arguments Details Value Author(s) References See Also Examples


Fits the iterative algorithm for DLMapping. Reads in data, performs detection and localization stages and outputs summary of selected QTL effects.


dlmap(object, phename, baseModel, algorithm=c("asreml", "lme"), fixed = NULL, 
random = NULL, rcov = NULL, sparse = NULL, pedigree, 
seed = 1, maxit=60, n.perm = 0, multtest=c("holm", "bon"), 
alpha = 0.05, filestem = "dl", ...)

## S3 method for class 'dlmap'
plot(x, chr, max.dist, qcol="light blue", mcol="red", pcol="purple", marker.names=FALSE, ...)

profileplot(object, ...)
## S3 method for class 'dlmap'
profileplot(object, chr, marker.names=TRUE, QTLpos=TRUE, pch=20, ...)

## S3 method for class 'dlmap'
summary(object, ...)



For input to dlmap, dlcross object created by create.dlcross; for plotting functions, object of class dlmap


Response variable name


Indicates whether to fit mixed models using asreml function or lme function (using packages asreml or nlme)


A formula object specifying the fixed effects part of the base model, with the terms, separated by + operators, on the right of a ~ operator. There is no left side to the ~ expression. If no fixed effect is specified, the model defaults to ~1, i.e. intercept only.


A formula object specifying the random effects part of the base model, with the terms, separated by + operators, on the right of a ~ operator. See asreml documentation for more detail.


A formula object specifying the error structure of the model, with the terms, separated by + operators, on the right of a ~ operator. See asreml documentation for more detail.


A formula object specifying the fixed effects to be absorbed, with the terms, separated by + operators, on the right of a ~ operator. See asreml documentation for more detail.


An alternative to specifying fixed, random, sparse, and rcov separately. If a base model has already been fit in asreml-R for the phenotypic variation, this can be input directly


Either a pedigree object consisting of three columns or a kinship matrix with number of rows and columns equivalent to the number of unique genotypes. For the pedigree, the first column is the individual ID, then the mother's ID and the father's ID. The name of the ID variable in the first column must match the idname variable. Rownames and colnames for the kinship matrix must match the idname variable.


Random number seed. Default=1


Number of permutations used to get adjusted p-values at each iteration of detection. If n.perm=0 (default) the Holm correction is used.


Correction used for multiple testing. If n.perm>0 will use permutation, but otherwise can choose between Holm and Bonferroni


Significance level for testing


Stem to add to names of any files generated in DL Mapping process. Default="dl"


Maximum number of iterations to attempt for convergence of lme


additional arguments


object of class dlmap


character string naming the subset of chromosomes to plot; or, if numeric, a vector of chromosome indices


a numerical value in cM determining the distance the genetic map should be subsetted by


colour of intervals surrounding QTL (see par for colour options)


colour of QTL flanking markers (see par for colour options)


colour of QTL positions (see par for colour options)


logical value. For profileplot, if TRUE then marker names are plotted along the top of the profileplot. Defaults to TRUE. For plot function, if TRUE then flanking marker names are highlighted. Defaults to FALSE


logical value. if TRUE then QTL positions are indicated with vertical lines in profileplot. Defaults to TRUE


Character to be used for points in plotting; default is solid circle


There are two versions of the main function, which use different engines to fit the linear mixed models which form the framework of the algorithm. Which is used depends on the value of the argument algorithm. algorithm="asreml" provides a much more general implementation of the DLMapping algorithm and is the preferred method of analysis. algorithm="lme" is more restricted in its capabilities, in that it cannot model random effects or covariance structure, cannot handle more than 200 markers, and only allows for a single phenotypic observation per genotype. Also, permutation has not been implemented for this function because it is very slow. However, this version will fit the basic algorithm and is useful should a license for ASReml not be available.

In studies where the number of genetic markers is much larger than the number of phenotyped individuals, we reduce the dimension of the analysis to the number of genetic lines used in the analysis multiplied by the number of chromosomes in the genetic map. This is done in a similar manner to wgaim, with thanks to Julian Taylor and Ari Verbyla for the suggestion. The transformation of the genetic data reduces the time for computational analysis for high-dimensional data and is particularly useful in association analysis.

This version of wgaim allows high dimensional marker information to be analysed. A simple transformation of the collated high dimensional marker set shows that it may be reduced to the number of genetic lines used in the analysis. This transformation is internal to the wgaim.asreml call and users can now expect a considerably large acceleration in the performance of wgaim.

In the asreml version, there are two options for specifying the model for phenotypic variation. The individual model components can either be input directly as they would be in an ASReml call, or a previous model (baseModel) output from ASReml can be input and the components will be retrieved from it. The latter formulation may be useful if prior phenotypic modelling has taken place. Note that in either case, variables appearing in the rcov statement must be ordered appropriately in the dataset. For example, if rcov=~ar1(Column):ar1(Row) the data must be sorted as Row within Column.

Missing values in asreml are replaced with zeros, so it is important to centre the covariate in question. This is done for all genotypes when algorithm="asreml". Thus individuals with phenotypic but not genotypic data, which play important roles in field trials, may be included safely. When algorithm="lme" these individuals cannot be included, so the default behavior is to omit observations with missing values.

It is recommended that n.perm be set to 0 for initial exploratory analysis, as the permutation analysis may be lengthy. The Holm correction is used to adjust for the number of chromosomes under consideration at each detection stage. While this is a conservative measure it seems to perform well in practice.

Two files are output with names set by the argument filestem, which has a default value of "dl". The file "filestem.trace" contains ASReml licensing and likelihood convergence output which otherwise would be dumped to the screen and possibly obscure other messages. Errors, warnings and other messages will still appear on the screen. Some warnings which appear may be passed through from an ASReml call and output on exit. These may generally be ignored. This file is not created if algorithm="lme" is used.

The file "filestem.det.log" is a record of iterations in the detection stage. For each iteration the REMLRT testing for genetic variation on each chromosome is output, along with adjusted p-values, genomewide threshold and markers selected as fixed effects. The p-values are corrected for the number of chromosomes tested either by the Holm correction or by permutation. If the number of permutations (n.perm) is greater than 0, then for the Xth iteration an additional file "filestem.permX" will be created which contains the test statistics for the permuted datasets. See the accompanying vignette for an example of how to interpret the ".det.log" file.

If the type of cross is not "other", the plotting function plots the genetic linkage map for a selection of chromosomes. Indicates marker locations, marker names, and detected QTL positions and associated flanking markers obtained from a dlmap fit. This function relies upon link.map.cross, which was written by Julian Taylor for the wgaim package. It is built upon here by adding QTL regions and estimated positions to the map.

The function plot.dlmap provides a neat visual display of chromosomes. If no QTL are detected, only the linkage map will be plotted; otherwise detected QTL will be placed at their estimated positions and the intervals around them (and flanking markers) will be highlighted. If a subset of chromosomes are plotted and detected QTLs exist outside that subset a warning will be given that QTLs have been omitted from the display.

The arguments mcol, qcol and pcol have been added for personal colour highlighting the flanking markers, QTL regions and QTL positions respectively. The procedure may also be given the usual col argument which will be passed on to the other markers.

In order to ensure that all marker names are displayed without vertical overlap, the default value of the "cex" parameter passed to "text" should be manipulated. For large maps with many chromosomes, marker names and adjacent chromosomes will overlap horizontally. In this case it is suggested that the user horizontally maximize the plotting window to remove overlap, or subset the chromosomes displayed.

The profileplot function plots the Wald statistic profile for each chromosome with detected QTL on first interval mapping scan. Indicates marker locations, marker names, and detected QTL positions obtained from a dlmap fit. It provides a neat visual display of the Wald profile for chromosomes with detected QTL. If no QTL are detected, nothing will be plotted. Otherwise, the Wald profile will be plotted by cM position of points on the interval mapping grid. Marker names will be displayed at the appropriate positions along the top of the plot. Vertical lines will mark the position of detected QTL.

The summary function outputs a summary of a dlmap object and detected QTL. It primarily prints the summary table computed from dlmap. This includes the chromosome QTL are detected on, estimated positions, flanking markers, QTL effects and standard deviations, Z-ratio and p-value.



Table with one row per QTL detected, columns for which chromosome the QTL is on, its position (cM), flanking markers, additive (dominant) effect and standard deviation, Z-ratio and p-value.


Total number of QTL detected on all chromosomes


Object of class asreml for final model containing all terms in the base model, as well as effects for every QTL detected at the appropriate locations. No random effects for markers are fit


If QTL are detected on C chromosomes, this is a list with C elements, each a matrix with 2 rows and a column for each position on the chromosome. The first row contains the cM position; the second row contains the Wald statistic for the model fit in the localization stage


Original dlcross input to the analysis


Emma Huang and Andrew George; Julian Taylor


Huang, BE and George, AW. 2009. Look before you leap: A new approach to QTL mapping. TAG 119:899-911

B. Emma Huang, Rohan Shah, Andrew W. George (2012). dlmap: An R Package for Mixed Model QTL and Association Analysis. Journal of Statistical Software 50(6): 1-22. URL http://www.jstatsoft.org/v50/i06/.

See Also



## Not run: 

# Convert cross object to DL Mapping format
dl.in1 <- dlcross(format="rqtl", genobj=BSdat, idname="ID", fixpos=1)

# Analyze data
BSdl <- dlmap(object=dl.in1, algorithm="lme", phename="phenotype", filestem="BS")


# With additional phenotypic data
dl.in2 <- dlcross(format="rqtl", genobj=BSdat, pheobj=BSphe, idname="ID", step=5)
BSph <- dlmap(object=dl.in2, algorithm="asreml", phename="phenotype", env=TRUE, random=~Block)


## End(Not run)

dlmap documentation built on May 2, 2019, 2:45 a.m.