T4 phage strains

[meesh]

Hi All,
I have been going crazy trying to find out how to begin answering the following. I've poured over my textbooks etc. and have really come up empty:

Two T4 phage strains differing in the alleles at three genes (p, q, and r) were used to simultaneously infect e. coli cells. The following progeny were observed:

p locus q locus r locus number
p + + 324
+ q + 85
p q + 55
p q r 6
+ q r 371
+ + + 10
+ + r 66
p + r 83

a) what are the genotypes of the parental phages in this cross?
b) what are the map distances between the genes and what is the gene order (draw a map)
ANY help would be appreciated

[blcr11]

Try looking at the sections that describe how Benzer analyzed the fine structure of genes using bacteriophage. The parental strains will be the most common product--it doesn't require any recombination event to create the parentals. Since it is obvious from the data what the parental genotypes are, your problem really is to deduce the gene order.

P.S. Don't assume that the alphabetical order (pqr) must correspond to the actual order. A priori, it can be any order--whatever the data says it is.

[meesh]

Ok, well I read some material on Benzer's studies and they were way over my head. This is supposed to be a question for a beginning class in genetics. I'm not even really sure what p, q, and r refer to. Are they genotypes?