Adding Annotations

Take a look at this plot:

It is very similar to the one you created in the previous exercise. In addition to the data, it shows a track called Genes with gene annotations. In what order would you execute the following code fragments to add this track to the plot?

Fragment 1

plotTracks(list(ideogram, cover_track,peak_track, tx, 
           GenomeAxisTrack()), chromosome="chr20", 
           from = start_pos, to=end_pos)

Fragment 2

tx <- AnnotationTrack(TxDb.Hsapiens.UCSC.hg19.knownGene, name="Genes")

Fragment 3

tx <- GeneRegionTrack(TxDb.Hsapiens.UCSC.hg19.knownGene, name="Genes")

Fragment 4

library(TxDb.Hsapiens.UCSC.hg19.knownGene)