Map Distance Calculator (centiMorgans)

In genetics, map distance measures how far apart two genes are on a chromosome — expressed in centiMorgans (cM) — based on how often they get separated during reproduction. Enter your recombination frequency (%) and total offspring counted, then select a calculation method (Standard, Kosambi, or Haldane) to get the map distance in cM, along with recombinant and parental offspring counts and a linkage classification.

%

Percentage of recombinant offspring observed

Total number of offspring analyzed in the cross

Results

Map Distance

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Recombinant Offspring

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Parental Offspring

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Linkage Classification

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Frequently Asked Questions

What is a centimorgan (cM) in genetics?

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.

How is map distance different from physical distance?

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.

When should I use the Kosambi vs Haldane mapping function?

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.

What does a recombination frequency of 50% indicate?

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.

How do I interpret the linkage classification results?

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.

Why is my calculated map distance less than the recombination frequency?

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.

What sample size is recommended for accurate mapping?

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.

Can map distance exceed 50 centiMorgans?

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.