Module 6 Lesson 9 - 2

Pedigree

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Read pages 610 - 616

A pedigree is a very useful tool for tracking the inheritance of traits. It is similar to a Punnett square, but instead of showing all possibilities, it shows only the phenotypes of actual parents and children. A pedigree is similar to a flowchart, illustrating many generations of people and their relationship to one another. By using the proper symbols, you can indicate the presence or absence of traits, and in doing so, construct a pattern that can be analyzed.

Although all patterns of inheritance you have studied can be analyzed with pedigrees, three primary types are studied in this lesson: autosomal dominant, autosomal recessive, and sex-linked traits. Read about tracing human genetics and constructing pedigrees in your text on pages 610 to 616.

Pedigree Conventions

Be sure to take good note of all possible symbols for pedigrees, which are also detailed at the top of page 612 of the textbook. These symbols are included in the data booklet provided during your exams. You do not need to memorize these symbols.

Squares represent males and circles represent females. The parents are connected by a horizontal line, and the children are connected to their parents by a vertical line. Siblings are connected to each other by a horizontal line originating from the parents, and siblings are placed from left to right according their birth order. Each generation is indicated by Roman numerals (I, II, III, IV, V, etc.).

When the given trait is expressed phenotypically, the individual is shaded. If the trait is not expressed, the symbol remains unshaded. In some pedigrees, individuals who do not express a recessive trait but are known to be heterozygous carriers of the trait are shown with a dot inside their unshaded symbol. However, carriers are not always identified in pedigrees. Lastly, deceased individuals have a diagonal line placed on their symbol in the pedigree. Deceased individuals are not always identified in pedigrees.