In some pedigrees, such as this one, the generations
are not numbered, only individuals. How can
individual 7 be unafflicted when both of his parents
are afflicted?
Since the trait is dominant, it is possible for his parents to be heterozygous (Bb). So they have the trait but they have a gene they can pass on with out it. If both of his parents Bb then he could’ve gotten both recessive and therefore not receive the trait
