Two methods of genetic recombination
Unlinked loci on
separate chromosomes (A & B
vs C) segregate independently according
to Mendel's Rules: the
recombination fraction is 50%.
Linked loci on the same
chromosome (A & B) do not
recombine, unless there is a physical exchange of genetic material as
the result of a crossover,
seen as a cytological chiasma
(plural, chiasmata).
Recombination frequency will be 0 ~
50%,
depending on whether or not a crossover occurs between the loci. This
is turn varies according to how closely the loci are situated.