If interference is complete or cent percent then thr frequency of observed double cross over will be

1) Equal to expected frequency

2) Greater than expected frequency

3) Lesser than expected frequency

4) Zero

Answer with proper explaination

In some regions of homologous chromoomes there are never any observed double recombinants. In these cases, Coefficient of Coincidence = 0, so I = 1 andinterferenceis complete.
Note :Interference (I) = 1 − c.o.c.
COC=(Observed Double Cross over/Expected Double Cross over).
If interference is complete then the Observed double cross over will be zero.