Differences in the satellite association pattern in the human population

The incidence and pattern of satellite association (sa) were studied in short‐term lymphocyte cultures in a group of 5 mentally retarded patients and in 11 controls. In 4 of the 5 patients a second sample was studied after 8 months. All individuals in both groups had normal karyotype. It was demonstrated statistically that the incidence of sa showed no significant heterogeneity among the controls but a highly significant heterogeneity among the patients. No heterogenity was observed between the two samples of each patient. In a total number of 2,020 sa complexes analysed, the largest comprised 7 chromosomes and several included more than 3 D or 2 G chromosomes; thus homologous chromosomes necessarily took part in the same sa complex. Both in the patient and in the control group, certain individuals showed significant deviations from the expected 5: 8: 2 ratio of DD, DG and GG associations and from the 3: 2 ratio of participating D and G chromosomes. In addition of the total number of cells with sa, the numbers of association complexes per cell as well as the D: G ratio showed significant heterogeneity among the patients but no heterogeneity between the two samples from each patient or among the controls. These results indicate the existence in the human population of differences in the formation of satellite associations.