Sex ratio under conditional sex expression.

We present a model to show that, when sex depends on environment rather than genotype, the sex expressed under relatively unfavorable conditions will be more abundant. This result refers to numbers of males and females in the population. By contrast, no clear prediction can be made about the allocation of resources to the two sexes. The model is constructed to highlight the logical relationship between the distribution of resources to the two sexes and the relative numbers of males and females. The predicted bias in numbers toward the sex developing under unfavorable conditions depends on the assumption that fitness either increases or decreases steadily according to the quantitative variable on which sex expression depends.