What does a pedigree indicate if affected individuals have no affected parents?

The observation that affected individuals have no affected parents typically suggests recessive inheritance. In a pedigree, if an individual has a condition but both of their parents are unaffected, it indicates that the affected individual must have inherited two copies of the recessive allele associated with the condition—one from each parent. The parents, being unaffected, must be carriers of the recessive allele, which means they each carry one recessive allele and one normal allele but do not express the trait themselves.

In contrast, dominant inheritance would generally show that at least one parent of an affected individual is also affected because a single dominant allele is sufficient to express the trait. X-linked conditions would be expected to manifest differently, particularly in how they are inherited from parent to offspring, often showing a pattern where affected males can only transmit the allele to daughters (if X-linked dominant) or where females can be carriers (in the case of X-linked recessive).

As such, the pattern of affected individuals having no affected parents is a hallmark characteristic of autosomal recessive conditions.