Genetics: A Conceptual Approach THIRD EDITION Copyright 2008 © W. H. Freeman and Company CHAPTER 6 Pedigree Analysis, Applications, and Genetic Testing Benjamin A. Pierce © 2009 W. H. Freeman and Company

Pedigree Analysis - pedigree analysis is a scrutiny of records of matings - pedigrees use standard sets of symbols to depict family trees and lineages - pedigrees provide concise and accurate records of families - pedigrees are helpful in following and diagnosing heritable traits (for example, diseases and medical conditions) by describing patterns of inheritance - pedigrees are useful in mapping (locating and isolating) genes “responsible” for certain traits

Pedigree construction - use standard set of symbols -one generation per row (oldest at the top) -siblings are shown in order of birth (from left to right) -generations are given Roman numerals (I, II, III, IV, etc) -individuals within a generation (row) are given Arabic numerals (1, 2, 3, 4, etc)

Analyzing pedigrees -trial and error: consider one pattern of inheritance at a time for each mating in the pedigree and try to find evidence against it; repeat for each pattern of inheritance, for example, autosomal recessive or dominant, X-linked recessive or dominant, etc -patterns of inheritance follow Mendelian rules; Mendelian ratios are rarely observed -assumption: for rare traits unaffected people entering into a family pedigree (for example, by marriage) are considered homozygous normal -result: pedigrees can frequently rule out, but not necessarily prove, a certain pattern of inheritance

I II III IV Autosomal recessive - the trait is found equally in both males and females -affected individuals usually have unaffected parents -the pattern of inheritance is often horizontal with several generations of unaffected individuals, but then several siblings in one generation are affected

I II III IV Autosomal dominant - the trait is found equally in both males and females -every affected individual has at least one affected parent -trait shows vertical pattern of inheritance, that is affected males and females are observed in each generation

The human pseudoachondroplasia phenotype is determined by a dominant allele D, that interferes with bone growth during development

The age of onset of Huntington disease

I II III IV X-linked recessive -more males than females are affected -all the sons of an affected mother will be affected -half the sons of a carrier mother will be affected -all daughters of carrier mothers will be normal, but half will be carriers -affected males do not transmit the trait to their sons -trait often skips a generation

I II III IV X-linked dominant -trait observed in both males and females -affected males ALWAYS transmit the trait to their daughters, but to NONE of their sons -affected females will transmit the trait to both sons and daughters -trait does not skip generation

I II III IV Y-linked -only males are affected -the trait is passed from an affected father to all of his sons

I II III IV Mitochondrial inheritance -both males and females are affected -the trait is passed from an affected mother to all her progeny -affected males do not transmit the trait to any of their progeny