I'm trying to make a Composite plot of multiple gene regions. I've read the vignette, Chapter 6 on doing this. I'm able to plot my data but not the GeneRegionTrack using.

chroms <- c("chr2", "chr17")             
ncols <- 1
nrows <- length(chroms)%/%ncols
grid.newpage()

pushViewport(viewport(layout = grid.layout(nrows,ncols)))

for (i in seq_along(chroms)) {
 pushViewport(viewport(layout.pos.col = ((i -1)%%ncols) + 1, layout.pos.row = (((i) -1)%/%ncols) + 1))
 plotTracks(list(mdTrack),chromosome = chroms[i], type= "histogram", showId = TRUE, stacking = "dense", lty.grid="dashed", add = TRUE)
 popViewport(1)
}

Is there a way to have multiple genes regions stored in in a single object? Right now I'm using the BiomartGeneRegionTrack to pull my gene region data

geneTrack <-BiomartGeneRegionTrack(genome = "hg38",
              symbol = c("DNMT3A","RAI1"),
              cex = 2,
              fontsize = 15,
              stacking = "squish",
              name = "Ensembl Genes v92",
              background.title = "grey",
              biomart=biomaRt::useMart(biomart="ensembl", dataset="hsapiens_gene_ensembl"))

However, this only stores the last gene. In this case RAI1

Is it possible to plot two (or more) gene regions at the same time?