Quantitative inheritance of red eye pigment in Drosophila melanogaster

1. The study deals with various aspects of quantitative inheritance of the red eye pigment in Drosophila inelanogaster. The pigment is extracted from individual flies and measured photometrically, and so it has been possible to handle this trait as a quantitative character by biometrical and other genetic methods.2. The interrelationships between pigment quantity, eye size and body size have been analysed. About 70% of the variance of pigment level is due to intrinsic differences in pigment production, while correlated variance is entirely a function of the eye size.3. Tests on the influence of major environmental differences suggest that the pigment per ommatidium is largely a function of the genotype and is little influenced by environmental variation.4. The estimates of the genetic and environmental contributions to the phenotypic variance and covariance have been derived from comparison of variability of an outbred population with that of crosses between inbred lines under optimal conditions; about 60% of the total variance is apparently due to genetic segregation. Both genetic and environmental factors contribute to the phenotypic correlations between pigment quantity and eye size and between eye size and body size.5. Two selection experiments for high and low pigment concentration based on phenotypic and family selection have been carried out for 8 generations to analyse the properties of genetic variation. The selection response suggests that about half the L netic variance is attributable to additive effects. The response. to selection shows a well defined asynnmetry in the two directions, selection being more effective for the low concentration.6. Crosses between three inbred lines differing greatly in 'pigment production and also exchange of homologous pair of chromosomes between two of them suggested that two recessive genes were fixed in one line on respectively chromosome II and III leading to 90. reduction in pigment, while one of the lines was homozygous for the second chromosome gene. These recessive effects combined entirely additively when single and joint substitution were compared.7. The results are considered in relation to the possible biological significance of differences in pigment per ommatidium