Relative thymus weight was estimated in C3H/He, C57BL/6 mice, their F1 and backcross hybrids, as well as in the progeny of complete diallel crosses between the BALB/c, C3H/He, C57BL/6 and AKR/J strains. On the basis of the analysis of these measurements, a conclusion is drawn that this character is inherited with incomplete dominance of smaller relative weight. The genes determining greater thymus weight are concentrated in the genetic pool of AKR/J and C57BL/6 strains. These genes are characterized by some degree of recessivity with respect to the genes determining smaller thymus weight which are concentrated in the genetic pool of C3H/He and BALB/c strains. The highest concentration of the "plus" and "minus" genes is found in the genetic pools of AKR/J and C3H/He strains respectively.

Ontogenetic changes of normal diploid cells and cells with genetic mutations (LHC-484 from a patient with xeroderma pigmentosum) have been studied under prolonged cultivation in a stationary phase. While investigating the dynamics of complex changes in certain cell properties and cell populations it was found that the cultivated human cells possess a particular pattern of ontogenetic changes for every culture and the dynamics of these changes depends upon the density of the cell population. Two cell subpopulations different in the degree of nucleus heterochromotinization have been discovered.

There has been obtained and is being maintained in vitro for over 12 years a stable cellular line DAPT, derived from a dedifferentiated human astrocytoma. In monolayer cultures the cells have passed 270 times. During 22 month (63 passages) the cells had a fibroblast-like shape, their growth having thereafter assumed an epithelioid character. On being impregnated with chlorous gold after Ramon-and-Kachal the cellular cytoplasma is stained purple-violet. In the periods of the fibroblast-like and epithelioid growth the time of the population doubling was 145 and 74 hours, respectively. The mitotic index amounted to 18%. When investigated during the 3d (106th passage) and 11th (250th passage) years of its cultivation the population consisted largely of cells containing 60-65 chromosomes. The carotype of the DAPT cells retained the main traits common to the structure of the human caryotype. After 7-9 months of cultivation (16-25th passages) the DAPT cells demonstrated the presence therein of an active glutamineketoacidic aminotransferase. Further on the activity of the enzyme declined. Factors influencing the changeability of the stable cellular DAPT line are discussed.