Enter your Recombination Frequency (%) and Total Offspring Counted, choose a Calculation Method, and the Map Distance Calculator converts your cross data into centiMorgans (cM) — along with a breakdown of Recombinant vs. Parental Offspring counts and a Linkage Classification for your gene pair.
Map Distance
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Recombinant Offspring
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Parental Offspring
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Linkage Classification
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A centimorgan (cM) is a unit of genetic distance that corresponds to a 1% recombination frequency between two loci. One map unit equals one centimorgan, named after geneticist Thomas Hunt Morgan.
Map distance (measured in cM) reflects the likelihood of recombination between loci, while physical distance measures actual DNA base pairs. Areas with high recombination rates have greater map distances despite shorter physical distances.
Use the Kosambi function when crossover interference is present (most organisms), as it accounts for reduced double crossovers. Use Haldane when there's no interference, such as in some fungi or when interference is negligible.
A recombination frequency of 50% indicates independent assortment, meaning the loci are either on different chromosomes or very far apart on the same chromosome (unlinked). This represents the maximum observable recombination frequency.
Closely linked (0-10 cM): genes are very close, rarely recombine. Moderately linked (10-30 cM): some recombination occurs. Loosely linked (30-50 cM): frequent recombination. Unlinked (50 cM): independent assortment.
When using mapping functions like Kosambi or Haldane, the calculated map distance accounts for undetected double crossovers, which can make the true genetic distance smaller than the observed recombination frequency.
Larger sample sizes provide more accurate estimates. Generally, at least 100-200 offspring are recommended for reliable mapping, though 1000+ offspring give the most precise results for detecting small recombination frequencies.
Yes, when using mapping functions that correct for multiple crossovers, map distances can exceed 50 cM even though recombination frequency cannot exceed 50%. This reflects the true genetic distance between loci.