Pedigree Analysis

A pedigree is a 'family tree' constructed using a standardised set of genetic symbols (Fig. 4.10) to record how a specific phenotypic trait has appeared, generation after generation, within one family line. Pedigree analysis is simply the systematic study of such charts — tracing whether a trait behaves as dominant or recessive, autosomal or sex-linked, by examining exactly which relatives are affected and which are not, and in what pattern.

This section also introduces the broader category that pedigree analysis is most often used to investigate: genetic disorders. A genetic disorder is any disease or syndrome caused by an abnormality in an individual's own DNA, and the scale of that abnormality can range enormously — from a single point mutation in one gene, all the way up to the gain, loss, or structural rearrangement of an entire chromosome or even a whole set of chromosomes. The chapter groups genetic disorders into exactly two categories on this basis: Mendelian disorders, caused by a single-gene mutation and inherited in the ordinary Mendelian pattern (covered next, in 4.8), and chromosomal disorders, caused by errors in chromosome number or structure (co …