The percentage of recombinant progeny produced in a cross is called the recombination frequency (or rate of recombination), which is calculated as follows:

In the testcross shown in Figure 5.6, 15 progeny exhibit new combinations of traits, so the recombination frequency is

Thus, 12.2% of the progeny exhibit new combinations of traits resulting from crossing over. The recombination frequency can also be expressed as a decimal fraction (0.122). TRY PROBLEM 9