Plot an error indicating the direction of phenotype specificity.
x-coordinate of the arrow.
x-coordinate of the arrow end.
y-coordinate of the arrow.
y-coordinate of the arrow end.
x-coordinates of the labels.
y-coordinates of the labels.
Labels for each end of the arrow.
Transparency of the labels.
Color for the label text.
Size of the labels.
Size of the arrow.
Colour of the arrow.
ggplot2 object.
plot_arrow()