The diagram opposite show a pair of homologous chromosomes during meiosis-


Maximum crossing over will occur between which genes.

The correct option is D A and d
An increase in distance between two genes increases the frequency of crossing over, while the closeness of the genes reduces the chances of crossing over. Since (A and d) and (a and D) are located farthest away from each other, maximum crossing over would occur between them.

So, the correct answer is option 'd'.