Sex-influenced characteristics are determined by autosomal genes and are inherited according to Mendel’s principles, but they are expressed differently in males and females. In this case, a particular trait is more readily expressed in one sex; in other words, the trait has higher penetrance in one of the sexes.

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For example, the presence of a beard on some goats is determined by an autosomal gene (B^b) that is dominant in males and recessive in females. In males, a single bearded allele is required for the expression of this trait: both the homozygote (B^bB^b) and the heterozygote (B^bB⁺) have beards, whereas the B⁺B⁺ male is beardless. In contrast, females require two bearded alleles in order for this trait to be expressed: the homozygote B^bB^b has a beard, whereas the heterozygote (B^bB⁺) and the other homozygote (B⁺B⁺) are beardless. The key to understanding the expression of the bearded gene is to look at the heterozygote. In males (for which the presence of a beard is dominant), the heterozygous genotype produces a beard, but in females (for which the absence of a beard is dominant), the heterozygous genotype produces a goat without a beard.

An extreme form of sex-influenced characteristic, a sex-limited characteristic, is encoded by autosomal genes that are expressed in only one sex; the trait has zero penetrance in the other sex. In domestic chickens, for example, some males display a plumage pattern called cock feathering. Other males and all females display a pattern called hen feathering. Cock feathering is an autosomal recessive trait that is limited to males. Because the trait is autosomal, the genotypes of males and females are the same, but the phenotypes produced by these genotypes are different in males and females. Only homozygous recessive males have the cock-feathering phenotype.