Inheritance Of Traits

Geneticists can study human genetic traits and trace genetic diseases from one generation to the next by studying the phenotypes of family members in a pedigree.


A pedigree is a diagram that shows how a trait is inherited over several generations. Figure 12-9 is a pedigree of a family that has several cases of cystic fibrosis. In a pedigree, squares stand for males and circles stand for females. A filled symbol means that the person has the trait or condition. An empty symbol means that the person does not have the trait or condition. A horizontal line joining a male and female indicates a mating. A vertical line indicates offspring arranged from left to right in order of their birth. Roman numerals label different generations.

O Female

© Female with trait or disease □ Male | Male with trait or disease Horizontal lines indicate matings.

Vertical lines indicate offspring (arranged from left to right in order of their birth).

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