Pedigree Analysis

Introduction– pedigree/family tree, can’t do genetic experiments with people, must wait for families to do crosses that show you the correct segregation pattern

We can determine most likely pattern based on what information we have, but it could change if we get new information – we must be flexible in our thinking.

Once we know pattern of segregation, these days we use (mostly) molecular methods or chromosome rearrangements to help us determine which chromosome and where on the chromosome the responsible gene is located. You will learn more about these approaches in more advanced genetics courses.

Symbols used:  Explain all symbols plus show a sample pedigree to show how the numbering works.

Mode of inheritance:

Features of each type of inheritance- with a focus on chromosome segregation rather than memorized rules. Maybe a series of a few pedigrees with “what can you rule out?” as the question. Once they can rule out, then of the remaining modes, which is more likely?  Talk about assumptions, and making the interpretation that requires the fewest assumptions, noting that it may not be the correct mode, but in the absence of additional information, we choose the interpretation requiring the fewest assumptions. i.e. if there is no EVIDENCE that people marrying into the family are carriers then you would not choose a mode of segregation that made them carriers. Example with a mother in the family, father outside, and vice versa to help show X vs autosomal recessive.

Notes; self-test questions after each section, and a series of pedigrees to interpret after as practice.

Glossary terms: dominant, recessive, autosomal, X-linked, pedigree, affected, carrier, proband, consanguinous.

Special modes: (not the main focus, but FYI)

Mitochondrial– inherited from mothers only

Y-linked: inherited father to son exclusively. From father to all sons and no daughters.