Interference

 The tendency of one cross over to inhibit another cross over in its adjacent region is called interference. The term interference was used by Muller. Sometimes, the occurrence of crossing over in one region enhances crossing over in adjacent regions, this phenomenon is called negative interference. The degree of interference may vary in different regions. The lesser the distance between genes, the greater is the interference and vice versa.

Interference is calculated as

Co-efficient of interference (%) = 1-coefficient of coincidence X 100. The term coincidence was used by Muller to explain the degree or strength of interference. The coefficient of coincidence is calculated by

If the observed double cross-over is equal to expected, the coefficient of coincidence will be 1 and zero interference.

If the observed double cross over is less than expected, the coefficient of coincidence will be less than 1 and interference will be positive

If the observed double cross-over is more than expected, the coefficient of coincidence will be

] more than 1 and interference will be negative.