Parental age dependent changes as a source of genetic variation in Drosophila melanogaster.

It has been shown repeatedly that numerous cumulative changes occur in chromosomes of D. melanogaster, as an effect of ageing which, especially in the homozygous state, significantly affect different fitness components of their carriers. It appears that the observed age-affected events are produced by systematic and ontogenetically programmed changes in genetic loads at specific chromosomes, which are transferable to following generations. It has been suggested that such changes could be of mutational origin, and that they could be more frequent at gene loci which are epigenetically active during ontogenesis. It was demonstrated that a large sample of identical chromosomes behave quite differently in the homozygous state when obtained from aged compared to non-aged parents, producing a significant decrease in relative viability, length of preadult development, and longevity of their carriers, as well as in the frequency of recombinations of corresponding chromosomes. A specific treatment by streptomycin resulted in remarkably milder effects of ageing, which is in accordance with the statement of some authors that such a treatment may diminish the frequency of spontaneous recessive mutations in their carriers. Thus the observed age-affected changes could be an important source of developmental and evolutionary variation of living organisms.