adding marker(snp-position) to the regional association plot

Question

[muralinmars]

Hi all,

I have a dataset for siginificant cpg probes (with p-value) associated with snps in a gene region... I managed to plot the data as a regional plot (in a span of 1mb region)..

Now I would like to add marker or SNP position to the plot... something like this.. (figure A)

here is the r code(from another source) ... that takes in the pvalues and the gene positions..

rectarrows <- function(x0,y0,x1,y1,height,length,...) {
  lwd=par("lwd")
  l0=height*(y1-y0)/sqrt((x1-x0)^2+(y1-y0)^2)
  l1=height*(x1-x0)/sqrt((x1-x0)^2+(y1-y0)^2)
  d0=length*(y1-y0)/sqrt((x1-x0)^2+(y1-y0)^2)
  d1=length*(x1-x0)/sqrt((x1-x0)^2+(y1-y0)^2)
  polygon(x=c(x0+l0,x1+l0-d1,x1,x1-l0-d1,x0-l0),y=c(y0-l1,y1-l1-d0,y1,y1+l1-d0,y0+l1),...)
}

pval<-runif(6000, 0, 1)
logPval<--log(pval,base=10)
pos=1:6000
rsID<-paste("rs",1:6000,sep="")
data<-as.data.frame(cbind(pos,rsID,pval,logPval))

genes <- c( "NFIA", "KANK4", "DOCK7", "L1TD1")
gene.start<- c(4, 350, 1000, 2100)
gene.end<- c(3004, 3350, 4000, 5010)
genes.pos<- as.data.frame(cbind(genes, gene.start, gene.end))

genes.pos[,1]=as.character(genes.pos[,1])
genes.pos[,2]=as.numeric(as.character(genes.pos[,2]))
genes.pos[,3]=as.numeric(as.character(genes.pos[,3]))

lay=layout(matrix(seq(2),2,1,byrow=TRUE),heights=c(2000,1000))
par(mar=c(0,4.1,4.1,2.1))
plot(x=as.numeric(data$pos),y=as.numeric(as.character(data$logPval)),xaxt="n")
par(mar=c(5.1,4.1,0.5,2.1))
plot(0,0,type="n",xlim=c(min(pos),max(pos)),ylim=c(0,length(genes)*1.1),yaxt="n")
lapply(seq(length(genes)), function(i) {
  rectarrows(genes.pos$gene.start[i],i,genes.pos$gene.end[i],i,col="blue",height=0.1,length=100) # change to length=1000 or length=10000 for large x-

axes, as this is the length of the 'arrow' part of the rectangle
  text(mean(c(genes.pos$gene.start[i],genes.pos$gene.end[i])),i+0.3,genes.pos$genes[i],cex=0.7)
})

Now how can I edit this to highlight the SNP marker in the plot (as shown in Figure A)?

Thanks
M