I was looking over some genetics question and came across this data set.

In the fruit fly Drosophila melanogaster there is a dominant gene b+ for grey body color and another dominant gene c+ for normal wings. The recessive alleles (b,c) of these two genes result in black body color and curved wings respectively. enter image description here

The question asked about calculation of the recombination frequency.

To me Ada's data set makes sense as the parental type offspring numbers are higher than the recombinant offspring. However, Donald's data set doesn't. Is there any way a recombinant offspring could be in a higher proportion than the parental type offspring?

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    $\begingroup$ can you give more info? which is the parental type? what is the experimental design? are these derived from the same background? what generation, e.g. F2? not enough info to answer as it is. This looks to me like a homework question, if so please add the "homework" tag. $\endgroup$ Sep 1, 2020 at 21:40
  • $\begingroup$ This isn't a homework question. In fact, this is a question from IBO. I'll actually post the whole information. $\endgroup$ Sep 1, 2020 at 22:49

1 Answer 1

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


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