Abstract
Chromosome arm lengths are the critical parameters of the human genome. The physical length is required to scale radiation hybrid and other maps to megabases. The genetic lengths in males and females are required for probabilities of exclusion and synteny, choice of well-spaced loci for linkage tests, and comparison with centromeric maps based on nondisjunction. Interpolation of new data into a map is possible only when the length is known, including the distances from centromere and telomeres to the nearest markers. Current evidence on physical parameters including the reliable measurements of relative lengths from flow cytometry but only a crude estimate of genome size (3200 megabases). Evidence on genetic parameters includes chiasma counts and linkage maps corrected for failure to sample telomeres, giving an autosomal size of 2809 centimorgans in males and 4782 centimorgans in females. Estimates of the physical and sex-specific genetic lengths are presented for each chromosome arm. Any linkage analysis that yields substantially larger estimates raises a suspicion of an inappropriate mapping function or typing errors.