# Recombination Frequency & Genetic Map Distance (cM) Convert recombination counts ↔ genetic distance with linear, Haldane (−½ln(1−2r)) and Kosambi (¼ln((1+2r)/(1−2r))) map functions, SE of r, and interval summation with predicted r. Derived from Sturtevant 1913, Haldane 1919, Kosambi 1944, Griffiths. Educational use only. > Canonical page: https://elysiatools.com/en/tools/recombination-frequency-map - **Category:** Education - **Keywords:** recombination frequency, genetic map distance, centimorgan, map function, haldane map function, kosambi map function, double crossover, linkage map, gene mapping, genetics ## Overview The Recombination Frequency & Genetic Map Distance calculator converts testcross counts into recombination frequency and genetic distance in centimorgans (cM), or sums map intervals and predicts the overall recombination frequency. It provides linear, Haldane, and Kosambi estimates, plus the standard error of r in counts mode. Educational use only. ## Inputs - **Calculation Mode** (select): From recombination counts, or from a list of map intervals. - **Recombinant count** (number): Recombinant offspring in a testcross (counts mode). - **Total progeny** (number): Total offspring scored (counts mode). - **Interval distances in cM** (text): Comma-separated adjacent interval distances in centimorgans (intervals mode). - **Decimal Places** (number) ## When to use - Calculate recombination frequency from recombinant offspring and total progeny counts. - Compare linear, Haldane, and Kosambi genetic map distances in cM. - Add adjacent map intervals and estimate the recombination frequency across the full span. ## How it works - Choose Counts → recombination & map distance or Map intervals → total distance & predicted r. - In counts mode, enter the recombinant count and total progeny; the calculator computes r as recombinant count divided by total progeny. - The result reports linear distance and map-function estimates from Haldane and Kosambi, with the standard error of r. - In intervals mode, enter comma-separated adjacent distances in cM; the calculator sums them and predicts r using the inverse Haldane and Kosambi functions. ## Use cases - Teaching linkage, crossing-over, double crossovers, and genetic map functions in genetics courses. - Checking recombination calculations from testcross or offspring-count exercises. - Building a linkage-map span by summing adjacent cM intervals and comparing predicted recombination frequencies. ## Frequently asked questions ### What is recombination frequency? Recombination frequency is the number of recombinant offspring divided by the total progeny, expressed as r or a percentage. ### What units does the calculator use for genetic distance? Genetic distance is reported in centimorgans (cM). One Morgan equals 100 cM. ### What is the difference between the Haldane and Kosambi estimates? Haldane assumes no interference, while Kosambi accounts for positive interference. For the same r, Haldane generally gives a larger distance than Kosambi. ### Why can map distance exceed 50 cM when recombination frequency cannot? Multiple crossovers can conceal recombination events, so r approaches 50% while mapping functions can estimate distances greater than 50 cM. ### Can this calculator be used for clinical or diagnostic decisions? 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