Coefficient of coincidence

The coefficient of coincidence is typically calculated from recombination rates between three genes.

The coefficient of coincidence is calculated by dividing the actual frequency of double recombinants by this expected frequency:[1] Interference is then defined as follows:[1] This figure tells us how strongly a crossover in one of the DNA regions (AB or BC) interferes with the formation of a crossover in the other region.

When three genetic markers, a, b and c, are all nearby (e.g. within the same gene) the coefficient of coincidence (calculated as in the above example) is generally found to be significantly greater than 1.

When the coefficient of coincidence is substantially greater than 1, it is known as “high negative interference".

High negative interference has been reported in bacteriophage T4 (e.g. [2][3] ) and in human immunodeficiency virus (HIV) infections.

DNA segment with three genes, showing a double recombination event. If the individual recombination rates (between A and B; and between B and C) are known, then the c.o.c. between the regions AB and BC can be calculated from the rate of double recombination.