Chapter 23, Problem 1CS

a.

Summary Introduction

To determine: The ways by which a dominant mutation originate a developmental malformation in some cases while nonpenetrant in others.

Introduction: In humans, HOXD genes are essential in limb development. An analysis of several families with malformations known as rocker bottom foot or claw foot revealed that rocker bottom foot has an autosomal dominant form of inheritance with variable expressivity and incomplete penetrance.

(b)

Summary Introduction

To determine: The ways by which variable expressivity leads in two different disorders from the same mutation.

Introduction: The penetrance of the mutation is defined as the percentage of individuals that show some degree of expression of the mutant genotype. By contrast, the expressivity defines the range of expression of the mutant genotype.