AN AID FOR PEDIGREE ANALYSIS Start by determining whether the trait is dominant or recessive. The following rules are designed to help you ask some useful questions about each pedigree you analyze. In the absence of evidence to the contrary, when evaluating a pedigree of a rare condition assume that individuals marrying into the pedigree are homozygous normals. I. DOMINANCE RELATIONSHIPS A dominant trait is the easiest to recognize, so begin by evaluating the pedigree for its fit to the predictions for dominant inheritance. If it does not fit these, then it is either a recessive trait or shows some complex aspect, such as incomplete penetrance. A. Dominant Traits 1. Reversing the typical Mendelian logic, remember that a dominant trait will not occur in an individual unless it also appears in at least one of the parents (exceptions occur in the case of a new mutation or of incomplete penetrance). 2. A fully dominant trait will not skip generations. It will therefore appear rather
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This note was uploaded on 04/28/2008 for the course BIO 13 taught by Professor Mclaughlin during the Fall '07 term at Tufts.