HWTernaryPlot: Ternary plot with the Hardy-Weinberg acceptance region

Description

HWTernaryPlot is a routine that draws a ternary plot for three-way genotypic compositions (AA,AB,BB), and represents the acceptance region for different tests for Hardy-Weinberg equilibrium (HWE) in the plot. This allows for graphical testing of a large set of markers (e.g. SNPs) for HWE. The (non) significance of the test for HWE can be inferred from the position of the marker in the ternary plot. Different statistical tests for HWE can be done graphically with this routine: the ordinary chisquare test, the chisquare test with continuity correction and the Haldane's exact test.

Usage

HWTernaryPlot(X, n = NA, addmarkers = TRUE, newframe = TRUE, hwcurve = TRUE, 
vbounds = FALSE, mafbounds = FALSE, mafvalue = 0.05, axis = 0, region = 1, 
vertexlab = colnames(X), alpha = 0.05, vertex.cex = 1, pch = 19, cc = 0.5, 
markercol = "black", markerbgcol = "black", cex = 0.75, axislab = "", 
verbose = FALSE, markerlab = NULL, markerpos = NULL, mcex = 1, connect =
FALSE, curvecols = rep("black",5), signifcolour = TRUE, patternsigsymbol = 19,
curtyp = "solid", ssf = "max", pvaluetype = "selome", grid = FALSE,
gridlabels = TRUE, patternramp = FALSE, axisticklabels = FALSE, ...)

Value

minp: minimum allele frequency above which testing for HWE is appropriate (expected counts exceeding 5).
maxp: maximum allele frequency below which testing for HWE is appropriate.
inrange: number of markers in the appropriate range.
percinrange: percentage of markers in the appropriate.
nsignif: number of significant markers (only if region equals 1,2 or 7.)

Arguments

X: a matrix of n genotypic compositions or counts. If it is a matrix of compositions, X should have (n rows that sum 1, and 3 columns, with the relative frequencies of AA, AB and BB respectively. Argument n should be supplied as well. If X is a matrix of raw genotypic counts, it should have 3 columns with the absolute counts of AA, AB and BB respectively. Argument n may be supplied and will be used for painting acceptance regions. If not supplied n is computed from the data in X.
n: the samples size (for a complete composition with no missing data).
addmarkers: represent markers by dots in the triangle (addmarkers=TRUE) or not
(addmarkers=FALSE).
newframe: allows for plotting additional markers in an already existing ternary plot. Overplotting is achieved by setting newframe to FALSE. Setting newframe = TRUE (default) will create a new ternary plot.
hwcurve: draw the HW parabola in the plot (hwcurve=TRUE) or not (hwcurve=FALSE).
vbounds: indicate the area corresponding to expected counts > 5 (vbounds=TRUE) or not (vbounds=FALSE).
mafbounds: indicate the area corresponding to MAF < mafvalue.
mafvalue: a critical value for the minor allele frequency (MAF).
axis: draw a vertex axis
0 = no axis is drawn
1 = draw the AA axis
2 = draw the AB axis
3 = draw the BB axis
4 = draw tick on the A-B axis
region: the type of acceptance region to be delimited in the triangle
0 = no acceptance region is drawn
1 = draw the acceptance region corresponding to a Chi-square test
2 = draw the acceptance region corresponding to a Chi-square test with continuity correction
3 = draw the acceptance region corresponding to a Chi-square test with continuity correction for D > 0
4 = draw the acceptance region corresponding to a Chi-square test with continuity correction for D < 0
5 = draw the acceptance regions for all preceding tests simultaneously
6 = draw the acceptance region corresponding to a Chi-square test with continuity correction with the upper limit for D > 0 and the lower limit for D < 0
7 = draw the acceptance region corresponding to a two-sided exact test
vertexlab: labels for the three vertices of the triangle
alpha: significance level (0.05 by default)
vertex.cex: character expansion factor for the labels of the vertices of the triangle.
pch: the plotting character used to represent the markers.
cc: value for the continuity correction parameter (0.5 by default).
markercol: vector with colours for the marker points in the triangle.
markerbgcol: vector with background colours for the marker points in the triangle.
cex: expansion factor for the marker points in the triangle.
axislab: a label to be put under the horizontal axis.
verbose: print information on the numerically found cut-points between curves of the acceptance region and the edges of the triangle.
markerlab: labels for the markers in the triangle.
markerpos: positions for the marker labels in the triangle (1,2,3 or 4).
mcex: character expansion factor for the labels of the markers in the ternary plot.
connect: connect the represented markers by a line in the ternary plot.
curvecols: a vector with four colour specifications for the different curves that can be used to delimit the HW acceptance region. E.g. curvecols=c("red", "green","blue","black","purple") will paint the Hardy-Weinberg curve red, the limits of the acceptance region for an ordinary chi-square test for HWE green, the limits of the acceptance region for a chi-square test with continuity correction when D > 0 blue and the limits of the acceptance region for a chi-square test with continuity correction when D < 0 black, and the limits of the exact acceptance region purple.
signifcolour: colour the marker points automatically according to the result of a signifance test (green markers non-siginficant, red markers significant). signifcolour only takes effect if region is set to 1, 2 or 7.
patternsigsymbol: plotting character used to represent significant makers when patternramp=TRUE
curtyp: style of the drawn curves ("dashed","solid","dotted",...)
ssf: sample size function ("max","min","mean","median",...). Indicates how the sample size for drawing acceptance regions is determined from the matrix of counts.
pvaluetype: method to compute p-values in an exact test ("dost" or "selome")
grid: draw a reference grid for genotype frequencies at (0.2,0.4,0.6,0.8)
gridlabels: if grid=TRUE plot labels at the grid
patternramp: paint a colour ramp for patterns of genotype frequencies. This will ignore signifcolour, and use colour to represent marker frequencies. The ramp is a green-red gradient for the relative frequency of the pattern.
axisticklabels: place numeric labels for allele frequencies on the A-B axis.
...: other arguments passed on to the plot function (e.g. main for a main title).

Author

Jan Graffelman jan.graffelman@upc.edu

Details

HWTernaryPlot automatically colours significant markers in red, and non-significant markers in green if region is set to 1, 2 or 7.

References

Graffelman, J. and Morales, J. (2008) Graphical Tests for Hardy-Weinberg Equilibrium Based on the Ternary Plot. Human Heredity 65(2):77-84.

Graffelman, J. (2015) Exploring Diallelic Genetic Markers: The HardyWeinberg Package. Journal of Statistical Software 64(3): 1-23. tools:::Rd_expr_doi("10.18637/jss.v064.i03").

Examples

Run this code

#
# Ternary plot with 1000 SNPs and HWE curve
#

X <- HWData(nm=1000,n=100)
HWTernaryPlot(X,100,region=0,vertex.cex=2,pch=1)

#
# Genotype frequency pattern of simulated SNPs with uniform
# allele frequency distribution
#

X <- HWData(nm=1000,n=100)
HWTernaryPlot(X,patternramp = TRUE)

#
# Genotype frequency pattern of simulated SNPs with skewed 
# allele frequency distribution
#

X <- HWData(nm=1000,n=100,shape1=1,shape2=20)
HWTernaryPlot(X,patternramp = TRUE)

#
# Genotype frequency pattern of SNPs simulated under HWE with
# allele frequency of 0.50
#

X <- HWData(nm=1000,n=100,p=0.25)
HWTernaryPlot(X,patternramp = TRUE)

#
# Genotype frequency pattern of SNPs simulated under HWE with
# allele frequency of 0.25
#

X <- HWData(nm=1000,n=100,p=0.25)
HWTernaryPlot(X,patternramp = TRUE)

#
# Genotype frequency pattern of SNPs simulated under HWE with
# allele frequency of 0.25, using a triangle to mark siginficant markers
#

X <- HWData(nm=1000,n=100,p=0.25)
HWTernaryPlot(X,patternramp = TRUE, region=1, patternsigsymbol = 2)

#
# Ternary plot of 1000 SNPs simulated under HWE and uniform allele frequency, with
# acceptance region for a chi-square test and significant markers in red.
#

X <- HWData(nm=1000,n=100)
HWTernaryPlot(X)

#
# Ternary plot of 100 SNPs simulated under HWE and uniform allele frequency, with
# acceptance region for an exact test and significant markers in red.
#

X <- HWData(nm=100,n=100)
if (FALSE) HWTernaryPlot(X,region=7)

Run the code above in your browser using DataLab