The Castle-Wright effective factor estimator gives a minimum estimate of the number of genes underlying complex traits. Because the Castle-Wright estimator does not rely on genetic markers, it is especially useful in genetically undeveloped species. In this article I describe two extensions of this estimator. The first corrects the estimator in heterogametic (XY) species with a partially sex-linked trait. In this case the traditional estimator underestimates gene number in F2 males and overestimates it in F2 females and backcross females and males. The second extension adapts the Castle-Wright equation to haplodiploid species.