What is the frequency of recombination between the a and b genes?

A geneticist isolates two mutations in bacteriophage. One mutation causes the clear plaques (c) and the other produces minute plaques (m). Previous mapping experiments have established that the genes responsible for these two mutations are 8 map units apart. The geneticist mixes phages with genotype c+ m+ and genotype c- m- and uses the mixture to infect bacterial cells. She collects the progeny phages and cultures a sample of them on plated bacteria. A total of 1000 plaques are observed. What numbers of the different types of plaques (c+ m+, c- m-, c+ m-, c- m+) should she expect to see?

The geneticist carries out the same experiment described in Problem 23, but this time she mixes phages with genotypes c+ m- and c- m+. What results are expected with this cross?

* 25. A geneticist isolates two r mutants (r13 and r2) that cause rapid lysis. He carries out the following crosses and counts the number of plaques listed here:

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