The remaining half of the gene pool for these traits will be unaffected by selection because they are hidden (unexpressed) in the genes of the other sex.
This term is restricted to autosomal traits, and should not be confused with sex-linked characteristics, which have to do with genetic differences on the sex chromosomes (see sex-determination system).
Sex-limited genes are also distinguished from sex-influenced genes, where the same gene will show differential expression in each sex.
Sex-limited genes are genes that are present in both sexes of sexually reproducing species but are expressed in only one sex and remain 'turned off' in the other.
In other words, sex-limited genes cause the two sexes to show different traits or phenotypes, despite having the same genotype.
He extensively explores this apparently sex-limited trait from a genetic perspective in this ground-breaking 50 page paper. Commonly hailed as one of the best evolutionary biologists of his time, Fisher was also a talented geneticist.