Recombination Frequency Calculator
Turning Crossover Counts Into a Genetic Map
Genes that sit close together on the same chromosome tend to be inherited as a block, since crossing over during meiosis is a random physical event and short distances give it little opportunity to separate two loci. Genes far apart on the same chromosome, by contrast, recombine almost as freely as genes on different chromosomes entirely. Counting how often offspring inherit a "recombinant" (non-parental) allele combination gives a direct, measurable estimate of the physical distance between two genes.
The Formula
Map Distance (cM) ≈ RF% (for small RF values)
One centiMorgan is defined as the genetic distance corresponding to a 1% recombination frequency — the correspondence holds well for loci that are close together, but breaks down for loci far enough apart that multiple crossovers between them become likely.
Worked Example
A cross producing 17 recombinant offspring out of 100 total: RF% = (17 ÷ 100) × 100 = 17%, giving an estimated map distance of approximately 17 centiMorgans.
Reading Recombination Frequency
| RF% | Interpretation |
|---|---|
| 0% | Completely linked — always inherited together |
| < 50% | Linked — on the same chromosome, some distance apart |
| 50% | Independent assortment — either on different chromosomes, or so far apart on the same chromosome that linkage is undetectable |
Where This Calculation Matters
- Genetic linkage mapping — building an ordered map of gene loci along a chromosome from a series of pairwise recombination frequencies.
- Marker-assisted selection in breeding — estimating how tightly a genetic marker is linked to a trait of interest, which determines how reliably the marker predicts the trait.
- Classical genetics coursework — the standard method taught for converting cross data into a linkage distance, historically pioneered by Alfred Sturtevant's fruit fly mapping work.
How to Use This Calculator
- Enter the number of recombinant offspring observed in the cross.
- Enter the total number of offspring produced.
- Select Calculate to get the recombination frequency and estimated genetic map distance in centiMorgans.
Related Calculations
Working from raw genotype counts instead? See the Allele Frequency Calculator, or model a specific cross directly with the Punnett Square Calculator.