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Recombination Frequency & Map Distance Calculator

Recombination frequency from parental and recombinant offspring counts, converted to map units (centimorgans) with the Haldane correction for double crossovers.

Parental type 1 count

Parental type 2 count

Recombinant type 1 count

Recombinant type 2 count

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How it works

RF = recombinants ÷ total; 1% RF = 1 cM; Haldane d = −50 ln(1 − 2RF)

Crossovers between two linked genes produce recombinant gametes, and the closer the genes, the rarer they are — so recombination frequency measures distance. Simple map units undercount at larger distances because double crossovers restore the parental arrangement; Haldane’s and Kosambi’s functions correct for that (Kosambi also allows for interference).

Worked example

192 recombinants out of 1,000 = 19.2% → 19.2 cM (Haldane 24.5 cM).

Frequently asked questions

Why can RF never exceed 50%?

Unlinked genes assort independently, giving 50% recombinants; more crossovers cannot push it higher. Above 50% means the classes were mislabelled.

How do I identify recombinant classes?

In a test cross the two most frequent phenotypes are parental; the two rarest are (single) recombinants.

Related calculators

Punnett Square Calculator

Cross two parent genotypes for a single gene and get the offspring genotype ratio, phenotype ratio and the odds of dominant versus recessive traits.

Dihybrid Cross Calculator

Cross two parents across two independent genes and get the phenotype ratio, the probability of each of the four trait combinations and the expected offspring counts for a chosen brood size.

Test Cross Ratio Calculator

Cross an organism of unknown genotype against a fully recessive tester and get the expected phenotype ratio, number of phenotype classes and offspring counts that reveal how many genes are heterozygous.

For teaching and planning — verify against your lab protocol and instrument documentation.