what is polymorphism (RFLP)?

Answer 1

Restriction fragment length polymorphism
http://en.wikipedia.org/wiki/Restriction_fragment_length_polymorphism

Answer 2

a rflp refers to a restriction fragment length polymorphism. These are sequences of DNA that are different from person to person, and they happen to occur where a particular restriction enzyme might cut. For instance one individual may have a mutation that results in a restriction site being created where as another individual will not. When run through gel electrophoresis this will result in the first individual having two smaller size pieces (travelling farther up the gel) and the second individual having one longer size strand (travelling less up the gel)