How to set different dot and dash sizes in plot

[Trastu]

I’m plotting two curves in one figure, using dash and dash-dot style; the 
result is hardly distinguishable as both dashes and dots are plotted in a very 
small size; changing the ‘markersize’ parameter doesn’t seem to make any 
difference.
How can I make them look a little bigger so they can be more easily seen?
Thanks,
David.