[Restriction fragment length polymorphisms in the families of patients with Down's syndrome (trisomy 21)].

Using the method of polymorphisms of lengths of restriction fragments (RFLP), the authors compare agreement and differences in the normal healthy Czech population and in families with a patient suffering from Down's syndrome. 2-alpha-satellite DNA probes were used which are weighed in the pericentromeric area of heterochromatin of the long arms of chromosomes 13 and 21. These probes contain a number of repetitive sequences, most frequently represented in human heterochromatin of the majority of chromosomes. By hybridization with an alpha-RI-6 probe multiallelic polymorphisms were obtained in families with Down's syndrome in five restrictive endonucleases (Bsp RI, Eco RI, Pst I, Taq I and Xba I). Restrictions with enzymes Bam HI and Hind III were non-polymorphous. Hybridization with the alpha-RI-IB probe revealed polymorphism with restrictive endonuclease Taq I. Enzymes Bam HI, Eco RI, Hind III, Pst I and Xba I (3) were non-polymorphous. The difference of the two probes in the centromeric area of chromosomes 13 and 21 was confirmed by hybridization in situ, using 3H-labelled thymidine triphosphate (TIP) in quantitative experiments on short-term cultures of lymphocytes of healthy subjects (4).