Hi,

I'm using gviz to plot some GWAS data and my DataTrack is showing the association p-values of SNPs  for a certain genomic region, which is a pretty basic dot plot. I would like to show certain significance levels on my plot, and add several horizontal lines with different colors (or at least different colors than my dots...). I tried abline parameter in the DataTrack function but didn't really help. Is there another way to add horizontal lines?

Also I want to add some horizontal grid lines to my DataTrack which is relatively easy to do by setting grid=T, v=0, h=10 , where the integer controls the number of lines, but how can I control the coordinates of these lines?

Thanks!

Solution I considered is to add grid grills firstly and then modify their positions , following is the code, but another problem occur:

library(Gviz)

########using the example data contained in Gviz 
data(twoGroups)
dat<-resize(twoGroups,width=1)
dat<-dat[,'control']
dTrack <- DataTrack(dat, name = "uniform")
plotTracks(dTrack,grid=T,col.grid='gray',v=0,h=5)

###############make some modification of the horizon grid lines
grid.edit('.grid.h.panel..',y0=unit(c(-5,0,5),'native'),y1=unit(c(-5,0,5),'native'),gp=gpar(col=c('red','green','blue')))

However, the horizon lines (the 5 and -5 horizon line)was not correctly placed. Is this due to the viewport where the points and grill lines were really plotted was not pushed ? And how can I push the viewport correctly? It looks like I can't get this information from the grid grill grob (in fact segmentsGrob):

grid.get('.grid.h.panel..')$vp