Quantitative analysis of X chromosome effects on the activities of the glucose 6-phosphate and 6-phosphogluconate dehydrogenases of Drosophila melanogaster.

By combining 20 X chromosomes with five autosomal backgrounds, the relative importance of these factors with respect to the activity variations of G6PD and 6PGD in Drosophila melanogaster were investigated. Analysis of variance revealed that there exist significant X chromosome, autosomal background and genetic interaction effects. The effect of the X chromosome was due mainly to the two allozymic forms of each enzyme, but some within-allozyme effects were also detected. From the estimated variance components, it was concluded that the variation attributed to the autosomal background is much larger than the variation attributed to the X chromosome, even when the effect of the allozymes is included. The segregation of the allozymes seems to account for about 10% of the total activity variation of each enzyme. The variation due to the interaction between the X chromosome and the autosomal background is much smaller than variations attributed either to the X chromosome or to the autosomal background. The interaction effect is indicated by the change of the ranking of the X chromosomes for different autosomal backgrounds. Highly significant and positive correlation between G6PD and 6PGD activities was detected. Again, the contribution of the autosomal background to the correlation was much larger than that attributed to the X chromosome.