Enter the total number of recombinant gametes and the total number of gametes into the Genetic Distance Calculator. The calculator will evaluate and display the Genetic Distance. 

From Counts
Map Function
r to cM
cM to r

Genetic Distance Formula

The following formulas are used to calculate genetic distance as a recombination fraction (r) or as a recombination percentage (%). 

\begin{aligned}
r &= \frac{RG}{G} \\
GD(\%) &= 100 \times \frac{RG}{G}
\end{aligned}
  • Where r is the recombination fraction (unitless, from 0 to 0.5)
  • GD(%) is the recombination percentage (from 0% to 50%)
  • RG is the total number of recombinant gametes (or recombinant offspring scored)
  • G is the total number of gametes (or total offspring scored)

To calculate the recombination fraction, divide the number of recombinant gametes by the total number of gametes. To express it as a percentage, multiply by 100. Note: for two loci, r cannot exceed 0.5 (50%). Also, using recombination percentage as “distance” (≈ cM) is only a good approximation for small distances because multiple crossovers can cause recombination to underestimate map distance; mapping functions (e.g., Haldane or Kosambi) are used to convert between r and map distance (cM).

How to Calculate Genetic Distance?

The following example problems outline how to calculate Genetic Distance.

Example Problem #1:

  1. First, determine the total number of recombinant gametes.
    • The total number of recombinant gametes is given as: 90.
  2. Next, determine the total number of gametes.
    • The total number of gametes is provided as: 250.
  3. Finally, calculate the Genetic Distance using the equation above: 

r = RG / G

The values given above are inserted into the equation below and the solution is calculated:

r = 90 / 250 = 0.36 (36%)

Example Problem #2: 

For this problem, the variables needed are provided below:

total number of recombinant gametes = 7

total number of gametes = 51

This example problem is a test of your knowledge on the subject. Use the calculator above to check your answer. 

r = RG / G = ?