Fluorescent chromosome polymorphisms: frequencies and segregations in a Dutch population

A study of the frequencies and segregation behaviour of fluorescent chromosome polymorphisms within a Dutch population is presented. The polymorphism patterns for chromosomes 1, 3, 4, 9, 13, 14, 15, 16, 21 and 22 were scored from 221 (108 female and 113 male) individuals with normal karyotype. Males and females were both found to carry an average of 4 polymorphic chromosomes per person, and approximately half of these were present in chromosomes No. 3 and 13. There was no significant difference between the frequencies per chromosome for the two sexes, and the data for chromosomes 3, 4, 14, 21 and 22 fitted a Hardy-Weinberg distribution. However, for chromosomes 13 and 15 an excess of heterozygotes and a lack of homozygotes was observed. Although the segregation behaviour of most chromosomes studied appeared to be mendelian, the segregation of chromosome No. 13 showed a lack of homozygotes without polymorphism. Possible mechanisms accounting for this effect are discussed.