Final answer:
Sex-influenced inheritance is when an allele is dominant in one sex and recessive in the other, often influenced by sex hormones and differentially expressed between males and females.
Step-by-step explanation:
For sex-influenced inheritance, a given allele is dominant in one sex and recessive in the opposite sex. This form of inheritance is influenced by the sex of the individual carrying the traits.
Sex-influenced inheritance involves genes that are autosomal (not located on the sex chromosomes) but their expression is modified by the sex hormones, resulting in different phenotypic expressions in males and females. An example of this type of inheritance is male pattern baldness, which is autosomally dominant in males but recessive in females. This means that a male only needs one copy of the allele for baldness to be bald, which he could receive from either parent, whereas a female would need two copies, one from each parent, to express the trait. Mendel's laws of inheritance still apply in terms of how alleles segregate into gametes and how they dominate or recede in the expression of traits. However, the influence of sex hormones creates a conditional expression of these traits, making them more likely to appear in one sex over the other.