THE LANSING EFFECT AND AGE-MEDIATED CHANGES IN GENETIC-PARAMETERS

The influence of variation in age of grandparents upon the heritability of two metric characters has been studied in the guppy (Poecilia reticulata) and Drosophilia melanogaster [caudal fin ray number and sternopleural chaeta number, respectively]. In both cases effects on heritability paralleling those already demonstrated to occur with variation in parental age were found and may be regarded as examples of Lansing effects. Analysis of components of variance of sternopleural bristle number in Drosophilia suggest that the genotypic variance for this character is increased in the progenies of older parents, largely as a consequence of an increase in additive genetiv variance. It appears probable that this results from age mediated changes in mechanisms of gene control. Both the effects described seem likely to be reflections of fundamental aspects of ageing processes in biological systems.