Sex-limited traits are genes that are present in both sexes of sexually reproducing species but are expressed in only one sex and have no penetrance, or are simply 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. These traits are restricted to autosomal traits, and should not be confused with sex-linked characteristics, which have to do with genetic differences on the sex chromosomes. Sex-limited genes are responsible for sexual dimorphism, which is a phenotypic difference between males and females of the same species regardless of genotype. These differences can be reflected in size, color, behavior (ex: levels of aggression), and morphology. An example of sex-limited genes are genes which control horn development in sheep: while both males and females possess the same genes controlling horn development, they are only expressed in males. The purpose of sex-limited genes is to resolve sexual conflict. These genes try to resolve the "push-pull" between males and females over trait values for optimal phenotype.