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.