Recombination Data Set
b+/c+
b/c
b+/c
b/c+




Ada
~0.39
~0.42
~0.08
~0.1


Donald
~0.09
~0.09
~0.4
~0.41




The other chromosome beeing b/c (I assume each one got an heterozygote fly and than they did a testcross)
There are a two possibilities for an heterozygote fly:
(b+/c+, b/c), (b+/c, b/c+)
If there was no genetic linkage we would except 0.25 for each fly group, but we didn't which means that fly groups with a higher probability are showing the original parental chromosomes phenotyping.
Since they didn't get the same results (by far) I assume (there are statistical tests for this) each scientist got a differently genetic fly
Donald got (b+/c+, b/c) since in his experiment the predominant flies are those showing a dominant phenotype and recessive phenotype and Ada got the mixed fly.
With this in mind we can see that the recombination frequency is 0.18 or 18cM
Yes, the recombinant can appear more than the parental (for example, if the parental is lethal or by pure chance) but in this case I belive it is simply a different organization on the chromosomes