SUMMARYSome current estimators of the relative viabilities of genotypes used in competition experiments, are shown to be biased, the bias being a function of the sample size and the gene frequency. From their use, an erroneous conclusion of a frequency-dependent phenomenon can be drawn. Almost unbiased estimators are advocated. The calculation of the exact distribution of these estimators for each experimental situation is the only correct way to test the significance of an observed value.

SUMMARYThe theoretical basis of the sexual selection and isolation indices W and Z, often used by investigators in analysing population cage experiments, is reexamined. Their expectations and variances, under the null hypothesis of no selection and random mating, are a function of the number N of the matings and are also frequency-dependent. The exact probability of W is given for any value of N. It appears that the peculiar properties of the distribution of W make its use misleading.

SummaryThe statistical properties of one estimetpr of absolute genetic distance (1/2) 2 I pzf-prf(, between two populations X and Y, are presented. It is shown that using this distance in small samples can be misleading particularly when populations are cloee Weach other.

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Two inhibitors of nucleotide metabolism, aminopterin and FUdR, were tested on a wild type strain, on two mutant strains: vg and vgnp, and on a vg strain with the wild type genetic background. Without inhibitors, a lengthening of the developing time was observed for the mutant strains compared to the wild type. With aminopterin, larval mortality and lengthening of developing time are significantly higher in the wild type than in the mutant strains. Mutant strains seemed to be resistant to low concentrations of FUdR. The hypothesis of a perturbed pyrimidine metabolism in the mutants seems to be confirmed.