MUTATION-RATE OF TRANSLOCATION VARIANTS O F DOWNS-SYNDROME IN LENINGRAD (1982-1991)

Karyological study of 644 newborns with Down's syndrome (DS) revealed 37 translocation cases (5.7%). Translocations were inherited in 8 case s, in 17 cases they were sporadic, and in 12 cases parents were not ex amined. Total mutation rate per gamete per generation (2.7 . 10) and m utation rates of D/21 and G/21 translocations in different female age groups were calculated. The obtained data are in good agreement with r esults of research in other world regions. Literature data on the pare ntal origin of de novo translocations for DS are presented. The role o f meiotic coorientation of nonhomologous chromosomes in anomalies of s permatogenesis is discussed.