In genetic pedigrees, what does it indicate if all affected individuals have an affected parent?

When all affected individuals in a genetic pedigree have an affected parent, it is indicative of dominant inheritance. In autosomal dominant disorders, an affected individual possesses at least one copy of the mutated gene, which means they can pass it onto their offspring. This pattern results in affected individuals appearing in every generation, as the trait can be transmitted from one parent to child.

In contrast, recessive inheritance typically involves affected individuals who can be born to unaffected parents if both parents are carriers of the recessive allele. Thus, you might observe unaffected carriers in previous generations. X-linked inheritance can show different patterns; for example, X-linked recessive conditions often affect males more than females and may have unaffected mothers who are carriers. X-linked dominant conditions would also show affected individuals with an affected parent but may have a different manifestation in terms of gender. Each of these forms of inheritance has distinctive patterns that clarify the type of genetic transmission occurring in a family, but when all affected individuals come from an affected parent, this strongly suggests a dominant mode of inheritance.