Thus, the genetic distance between ss and e is 12.2 m.u.

Finally, calculate the genetic distance between the outer two loci, st and e. Add up all the progeny with crossovers between the two loci. These progeny include those with a single crossover between st and ss, those with a single crossover between ss and e, and the double crossovers ( st+ / ss / e+ and st / ss+ / e ). Because the double crossovers have two crossovers between st and e, we must add the double crossovers twice to determine the recombination frequency between these two loci:

st- e recombination frequency =

Notice that the distances between st and ss (14.6 m.u.) and between ss and e (12.2 m.u.) add up to the distance between st and e (26.8 m.u.). We can now use the map distances to draw a map of the three genes on the chromosome:

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