The Systematic Location of Genes by Means of Crossover Observations

IN the construction of a chromosome map, the distances between neighboring genes are equated to the percentage of crossovers which have been observed between them. Owing to errors of random sampling, and sometimes to other disturbing causes, inconsistencies always arise between the distances so determined. For example, in the important data given by Lancefield and Metz for the sex chromosome of Drosophila willistoni [1, p. 241] we have the following values: