In some organisms, traits are influenced by sex of the organism. In other words, male and female individuals, which are genotypically similar for a particular trait, give different expressions of the same trait, thus demonstrating that the trait is influenced by sex. Such traits are called sex-influenced traits. This can be illustrated with the help of example of horns in sheep, which are effectively controlled by a single gene, since other genes controlling this trait are always homozygous. Among Dorset sheep, both sexes are horned and homozygous (h⁺h⁺). In Suffolk sheep, both sexes are hornless and homozygous recessive (hh). When Dorset (horned) are crossed to Suffolk (hornless), the F₁ (h⁺h)are found to be horned males and hornless females. When F₁'s (h⁺h)are intercrossed, in the resulting F₂ progeny, males segregated as 3 (horned) to 1 (hornless), while females segregated as 1 (horned) to 3 (hornless). It is thus obvious that expression of only heterozygote (h⁺h)is influenced by sex, h⁺h being horned in male and hornless in female (Table 16.1). In other words, while horned character is dominant in male, it is recessive in female. This influence is believed to be mainly due to male and female hormones.