The recombination frequency with respect to genes P and Q is 15%, Q and R is 11% and P and R is 4%. The possible sequence of linked genes on a chromosome must be 
I. P, Q, R                           II. Q, P, R 
III. P, R, Q                        IV. Q, R, P
 

More is the recombination frequency with respect to two genes, more far away are the genes and lesser is the recombination frequency, closer are the genes. Since the Recombination frequency with respect to P and Q genes is 15%, P is present towards one end of chromosome and Q at the other end. Recombination frequency with respect to Q and R is 11% and P and R is 4% clear shows that R is nearer to P than Q and located between P and Q. Hence the sequence of genes from one end to another end is P, R and Q. From the another end to the first end it is Q, R, P.