Abstract

The up-to-date state of human cytogenetics allows to turn back to hypothesis of distributive pairing as a strongly fruitful for resolving a number of problems concerning etiology of chromosome aneuploidy. Distributive pairing could account for such phenomena as: 1. Prevalence of nondisjunction (ND) in the first meiosis, compared with the second; 2. Excess of males among children with the Down syndrome; 3. Recurrent cases of aneuploidy, including aneusomies for different chromosomes; 4. Appearance of individuals with double aneusomies; 5. High recurrent risk for young parents; 6. Increased chance of ND for chromosomes not involved in rearrangement in carriers of balanced translocations; 7. Increased frequency of ND of autosomes in individuals with quantitative and structural sex chromosome anomalies; 8. The role of heterochromatic regions in ND; 9. Increased frequency of spontaneous abortions in couples having children with chromosome anomalies and in persons with unusual heterochromatic variants. The hypothesis could predict: 1. Essential contribution of errors in gonial cells to the origin of aneuploidy; 2. Important role of the factors influencing the prophase; 3. The possibility of offering forecast for sex chromosome anomalies rate on the basis of trisomy 21 rate, due to the fact that both autosomal and gonosomal aneuploidies have to be induced by the same factors.