Intervals in genetic maps may be expressed in recombination fractions or map units. The method of combining adjacent intervals depends on the manner of expressing the intervals.
For interval A-C composed of intervals A-B and B-C, if the adjacent intervals are measured in recombination fractions:
recombination fraction for A-C =
= ((recombination fraction for A-B) * (1 - (recombination fraction for B-C))) + ((recombination fraction for B-C) * (1 - (recombination fraction for A-B))) =
= (recombination fraction for A-B) + (recombination fraction for B-C) - (2 * (recombination fraction for A-B) * (recombination fraction for B-C))
where:
• recombination fractions are decimal fractions
If the adjacent intervals are measured in map units (typically centiMorgans, or cM), then the intervals can simply be added together:
distance A-C in centiMorgans =
= (distance A-B in centiMorgans) + (distance B-C in centiMorgans)
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