No abstract

No abstract

To test for different gene activity during ageing, an experiment was set up to determine whether or not genetic variation and genetic correlations between fitness traits at different ages change in a systematic way through time. Additive genetic and environmental variance components as well as genetic correlations between different age periods were calculated for the fitness trait "number of adult offspring" in a population of Drosophila melanogaster. Genetic correlations between age periods were all positive and, hence, did not support the theory postulating that genes with beneficial effects on early fitness have pleiotropic unfavourable effects on late fitness. The environmental variation as well as the additive genetic variance showed a clear increase with age. The increase of environmental variation is probably a result of the individuals' increasing difficulties in coping with environmental stress due to physiological deterioration with age. Increased additive genetic variation may be explained by more and more genes being "turned on" with age. Alternatively, it could be caused by accumulation of deleterious mutations with different effects and may reflect the individuals' capacity of DNA repair.

No abstract

The effect of ethyl methane sulfonate-induced mutations in different germ cell stages on male reproductive fitness at early and late age, compared to an untreated control, was investigated in a laboratory population of Drosophila melanogaster. Indication of active DNA repair processes after mutagen treatment was obtained in the pre-meiotic germ cell stages. Genetic parameters for the male fitness trait, ie "number of progeny" were estimated in a succession of different broods at early and late ages. Heritability estimates for progeny size were found to vary between 0.13 and 0.97 in the different brood stages and over the 2 treatment groups. The estimates of genotype-environment interaction, as well as genetic correlations, suggest that the genetic determination of progeny size is different at an early age between EMS-treated and untreated individuals, but not at late ages. reproductive fitness / Drosophila melanogaster / genetic parameter / ageing / mutagen Résumé-Évaluation génétique des capacités de reproduction de mâles de différents âges exposés à un agent mutagène chez Drosophila melanogaster. Les ef jets des mutations induites par l'éthyl méthanesulfonate (EMS) au cours des différentes phases de la gamétogenèse sur la capacité de reproduction de mâles, jeunes ou âgés, ont été étudiés sur une population de laboratoire de Drosophila melanogaster. Des processus actifs de réparation de l'ADN, après traitement par l'EMS, existent vraisemblablement au cours des phases préméiotiques. Les paramètres génétiques relatifs au nombre de descendants par mâle ont été estimés dans plusieurs séries de ponte correspondant à différents âges. Les estimations de l'héritabilité de ce caractère varient de 0,17 à 0,67 dans les différentes séries de ponte et dans les deux groupes de mâles traités et non traités. Les estimations des interactions génotype-milieu, ainsi que des corrélations génétiques suggèrent que le déterminisme génétique du nombre de descendants est différent chez les jeunes mâles * Correspondence and reprints exposés à l'EMS par rapport aux mâles non traités. En revanche, aucune différence n'est détectée chez les mâles plus âgés. capacité de reproduction / Drosophila melanogaster / paramètre génétique / vieillissement / mutagène