What is the genotype with lowest frequency?

[TytoAlba95]

Homework Statement:

NA

Relevant Equations:

The right answer is (d).

But unlike the Q which asks which one has the least frequency, I think the frequency of this genotype (d) will be 0%. Because it is not possible to transform the recipient bacterial DNA with a DNA segment where only two terminal genes recombine but the central gene does not.
Please clarify if I'm wrong.

 

[Ygggdrasil]

Homework Statement:: NA
Relevant Equations:: The right answer is (d).

But unlike the Q which asks which one has the least frequency, I think the frequency of this genotype (d) will be 0%. Because it is not possible to transform the recipient bacterial DNA with a DNA segment where only two terminal genes recombine but the central gene does not.
Please clarify if I'm wrong.

View attachment 263135

It is possible for multiple crossover events to occur during recombination. See for example, figure 9-10 in https://www.ncbi.nlm.nih.gov/books/NBK21351/#_A1413_