抄録
Three hundred pairs were sampled from a population of D. melanogaster collected from Katsunuma in 1963 and maintained in laboratory. They were selected to both photopositive and photonegative directions during fifteen generations. These two populations responded effectively to the selections, and the realized heritability of both populations for the first 10 generations was estimated similarly to be about 3 per cent.
These populations were relaxed after fifteen generations of selection, and their positive or negative phototactic behaviors were returned to their initial states after only seven generations. This phenomena could be ascribed to the genetic homeostasis formed by the natural selection.
The frequency of deleterious second chromosomes and adult emargence rhythm in these phototactic populations were analysed. The frequency of lethal and semilethal chromosomes in the photopositive population was 43%, and those for the photonegative and the unselected populations were 18% and 27%. The correlation between the frequency of lethal genes and photopositive character was confirmed by the photopositive behavior of lethal heterozygotes (li/lj or l/OR).
Adult emergence rhythm of photonegative flies was not observed even under the periodical light and dark environment (LD 12:12). Mean developmental time (from egg to adult) of photonegative flies was longer than photopositive and unselected flies.
