Gene expression and developmental rate

Abstract

InD. melanogaster the genessc, D, L andvg were used to demonstrate the extragenic transmission of factors which change the expression of these genes.

Many environmental conditions such as composition of the food influence the developmental rate which in turn can be shown to be primarily responsible for changing the expression of the genes.

Genetic modifiers may act indirectly on the expression of these genes by changing the degree of fertility which, through relative crowding, may change the developmental rate.

There is a parental effect which is presumably due to the size of the egg determining the developmental rate, environmental influences producing larger or smaller flies and thus determining the expression of the genes in the following generation.

There is a grandparental effect which can be shown to be transmitted through the sperm and which usually determines the expression of the genes more strongly than the parental effect.

The results can best be explained on the assumption that the various influences change the rate of reproduction of heterochromatic DNA in relation to euchromatic DNA and that, through extragenic transmission, these changes persist for at least two generations.