Alfred Sturtevant used the frequency of recombination between gene pairs to map their position on the chromosome . 1 map unit (centimorgan) equals 1% recombination frequency. However, the maximum recombination frequency between any two genes cannot exceed 50% (which indicates independent assortment). Even if the map distance (calculated by summing small intervals) is greater than 50 units (e.g., 66 units), the observable recombination frequency between the distant markers will saturate at 50%.